Content:

CR – Cryospheric Sciences

CR1.1 – Ice sheet mass balance and sea level: ISMASS/ISMIP6

The Greenland ice sheet is one of the largest contributors to global-mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater runoff and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of CMIP5 global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100 with contributions of 89 ± 51 mm and 31 ± 16 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the southwest of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against a unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 mm and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean.

How to cite: Goelzer, H. and the The ISMIP6 team: The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2682, https://doi.org/10.5194/egusphere-egu2020-2682, 2020.

EGU2020-11241 * | Displays | CR1.1 | Highlight

Quantifying uncertainties in the land ice contribution to sea level from ISMIP6 and GlacierMIP

Tamsin Edwards and the ISMIP6, GlacierMIP and friends

The land ice contribution to global mean sea level has not yet been predicted for the latest generation of socio-economic scenarios, nor with coordinated assessment of uncertainties from the various computer models involved (climate, Greenland and Antarctic ice sheets, and global glaciers). Two recent projects generated a large suite of projections but used previous generation scenarios and climate models and could not fully explore uncertainties. Here we estimate probability distributions for their projections, using statistical emulation, and find uncertainty does not diminish if greenhouse gas concentrations are reduced: the sea level contribution of land ice is 28 [5, 57] cm from 2015 to 2100 under no mitigation (median and 90% range), and 16 [-5, 46] cm under very stringent mitigation. Greenland is projected to contribute around 2.5 cm/ºC of global warming, and Alaskan and Arctic glaciers a total of around 2 cm/ºC, but Antarctic uncertainties are too large to determine temperature-dependence. Knowing future global mean temperature exactly for a given socio-economic scenario would reduce the uncertainty for glaciers by up to two thirds (6 cm) but have little effect for ice sheets. Quantifying how ice sheet margins respond to ocean warming would reduce uncertainty by up to one third (Antarctica 15 cm; Greenland 7 cm). The remaining uncertainty for a given scenario is dominated by the climate and glaciological models themselves. Improved modelling and observations of polar regions, rather than global warming and glaciers, would therefore have the greatest effect in reducing uncertainty in future sea level rise.

How to cite: Edwards, T. and the ISMIP6, GlacierMIP and friends: Quantifying uncertainties in the land ice contribution to sea level from ISMIP6 and GlacierMIP, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11241, https://doi.org/10.5194/egusphere-egu2020-11241, 2020.

EGU2020-18037 | Displays | CR1.1

Comparison of the surface mass and energy balance of CESM and MAR forced by CESM over Greenland: present and future

Charlotte Lang, Charles Amory, Alison Delhasse, Stefan Hofer, Christoph Kittel, Leo van Kampenhout, William Lipscomb, and Xavier Fettweis

We have compared the surface mass (SMB) and energy balance of the Earth System model (ESM) CESM (Community Earth System Model) with those of the regional climate model (RCM) MAR (Modèle Atmosphérique Régional) forced by CESM over the present era (1981 — 2010) and the future (2011 — 2100 with SSP585 scenario).

Until now, global climate models (GCM) and ESMs forcing RCMs such as MAR didn’t include a module able to simulate snow and energy balance at the surface of a snow pack like the SISVAT module of MAR and were therefore not able to simulate the SMB of an ice sheet. Evaluating the added value of an RCM compared to a GCM could only be done by comparing atmospheric outputs (temperature, wind, precipitation …) in both models. CESM is the first ESM including a land model capable of simulating the surface of an ice sheet and thus to directly compare the SMB of an RCM and an ESM the first time.

Our results show that, if the SMB and is components are very similar in CESM and MAR over the present era, they quickly start to diverge in our future projection, the SMB of MAR decreasing more than that of CESM. This difference in SMB evolution is almost exclusively explained by a much larger increase of the melter runoff in MAR compared to CESM whereas the temporal evolution of snowfall, rainfall and sublimation is comparable in both runs.

How to cite: Lang, C., Amory, C., Delhasse, A., Hofer, S., Kittel, C., van Kampenhout, L., Lipscomb, W., and Fettweis, X.: Comparison of the surface mass and energy balance of CESM and MAR forced by CESM over Greenland: present and future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18037, https://doi.org/10.5194/egusphere-egu2020-18037, 2020.

EGU2020-6943 | Displays | CR1.1

Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term

Nanna Bjørnholt Karlsson, Anne Munck Solgaard, Kenneth D. Mankoff, Jason E. Box, Michele Citterio, William T. Colgan, Kristian K. Kjeldsen, Niels J. Korsgaard, Baptiste Vandecrux, Douglas Benn, Ian Hewitt, and Robert S. Fausto

The Greenland ice sheet has been one of largest sources of sea-level rise since the early 2000s. The total mass balance of the ice sheet is typically determined using one of the following methods: estimates of ice volume change from satellite altimetry, measurements of changes in gravity, and by considering the difference between solid ice discharge and surface mass balance (often referred to as the input–output method). In spite of an overall agreement between the different methods, uncertainties remain regarding the relative contribution from individual processes, and to date the basal melt has never been explicitly included in total mass balance estimates. Here, we present the first estimate of the contribution from basal melting to the total mass balance. We partition the basal melt into three terms; melt caused by frictional heat, geothermal heat and viscous heat dissipation, respectively. Combined, the three terms contribute approximately 25 Gt per year of basal melt to the total mass loss equivalent to 5% of the average solid ice discharge (average value of 1986-2018 discharge). This is equivalent to the ice discharge from the entire northeastern sector. We find that basal melting also accounts for between 5% and 30% of observed thinning in most major glacier outlets. Over our observation period (winter 2017/18), close to 2/3 of the basal melt is due to frictional heating from fast moving ice. This term is expected to increase in the future, as ice streams are likely to expand and speed up in response to rising temperatures.

How to cite: Karlsson, N. B., Solgaard, A. M., Mankoff, K. D., Box, J. E., Citterio, M., Colgan, W. T., Kjeldsen, K. K., Korsgaard, N. J., Vandecrux, B., Benn, D., Hewitt, I., and Fausto, R. S.: Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6943, https://doi.org/10.5194/egusphere-egu2020-6943, 2020.

EGU2020-11738 | Displays | CR1.1

Progress towards coupling ice sheet and ocean models

Ben Galton-Fenzi, Rupert Gladstone, Chen Zhao, David Gwyther, John Moore, and Thomas Zwinger

With recent developments in the modelling of Antarctica and its interactions with the ocean several coupled model frameworks now exist.  This talk will focus on presenting the Framework for Ice Sheet - Ocean Coupling (FISOC), developed to provide a flexible platform for performing coupled ice sheet - ocean modelling experiments. We present progress and preliminary results using FISOC to couple the Regional Ocean Modelling System (ROMS) with Elmer/Ice, a full-Stokes ice sheet model. Idealised experiments have been used that also contribute to the WCRP Marine Ice Sheet-Ocean Model Intercomparison Project (MISOMIP).  A recent focus is on testing emergent behaviour of the coupled system and the model numerics. The talk will outline future technological applications and developments conducted as part of a broader international consortium effort. These efforts include coupling to sub-glacial hydrology, sea ice and atmospheres to form a complete system-downscaling technology from which to examine the influence of future climate on ice sheet evolution and hence sea level and global climate impacts. Developments to apply the technology to the Greenland Ice Sheet are presently underway.

How to cite: Galton-Fenzi, B., Gladstone, R., Zhao, C., Gwyther, D., Moore, J., and Zwinger, T.: Progress towards coupling ice sheet and ocean models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11738, https://doi.org/10.5194/egusphere-egu2020-11738, 2020.

EGU2020-20029 | Displays | CR1.1

The role of history and strength of the oceanic forcing in sea-level projections from Antarctica with the Parallel Ice Sheet Model

Ronja Reese, Anders Levermann, Torsten Albrecht, Hélène Seroussi, and Ricarda Winkelmann

Mass loss from the Antarctic Ice Sheet constitutes the largest uncertainty in projections of future sea-level rise. Ocean-driven melting underneath the floating ice shelves and subsequent acceleration of the inland ice streams is the major reason for currently observed mass loss from Antarctica and is expected to become more important in the future. Here we show that for projections of future mass loss from the Antarctic Ice Sheet, it is essential (1) to better constrain the sensitivity of sub-shelf melt rates to ocean warming, and (2) to include the historic trajectory of the ice sheet. In particular, we find that while the ice-sheet response in simulations using the Parallel Ice Sheet Model is comparable to the median response of models in three Antarctic Ice Sheet Intercomparison projects – initMIP, LARMIP-2 and ISMIP6 – conducted with a range of ice-sheet models, the projected 21st century sea-level contribution differs significantly depending on these two factors. For the highest emission scenario RCP8.5, this leads to projected ice loss ranging from 1.4 to 4.3 cm of sea-level equivalent in the ISMIP6 simulations where the sub-shelf melt sensitivity is comparably low, opposed to a likely range of 9.2 to 35.9 cm using the exact same initial setup, but emulated from the LARMIP-2 experiments with a higher melt sensitivity based on oceanographic studies. Furthermore, using two initial states, one with and one without a previous historic simulation from 1850 to 2014, we show that while differences between the ice-sheet configurations in 2015 are marginal, the historic simulation increases the susceptibility of the ice sheet to ocean warming, thereby increasing mass loss from 2015 to 2100 by about 50%. Our results emphasize that the uncertainty that arises from the forcing is of the same order of magnitude as the ice-dynamic response for future sea-level projections.

How to cite: Reese, R., Levermann, A., Albrecht, T., Seroussi, H., and Winkelmann, R.: The role of history and strength of the oceanic forcing in sea-level projections from Antarctica with the Parallel Ice Sheet Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20029, https://doi.org/10.5194/egusphere-egu2020-20029, 2020.

EGU2020-20660 | Displays | CR1.1

Trends and projections in ice sheet mass balance

Andrew Shepherd and the The IMBIE Team

In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. Since the early 1990’s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance.  Cumulative ice losses from both ice sheets have been close to the IPCC’s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.

How to cite: Shepherd, A. and the The IMBIE Team: Trends and projections in ice sheet mass balance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20660, https://doi.org/10.5194/egusphere-egu2020-20660, 2020.

EGU2020-5747 | Displays | CR1.1

Interpretation and Analysis of Projected Ice Sheet Contributions from a Structured Expert Judgement

Willy Aspinall, Roger Cooke, Bob Kopp, Jon Bamber, and Michael Oppenheimer

Despite considerable advances in process understanding, numerical modeling and the quality of the observational record of ice sheet contributions to sea level rise (SLR) since the last IPCC report (AR5), severe limitations remain in the predictive capability of numerical modeling approaches. In this context, the potential contribution of the ice sheets remains the largest uncertainty in projecting future SLR beyond mid-century. Various approaches, including Monte Carlo ensemble emulator simulations, probabilistic or plausibility methods, and Semi Empirical Models have been used in attempts to address these limitations. To explore and quantify the uncertainties in ice sheet projections since the AR5, a Structured Expert Judgement (SEJ) elicitation – involving 23 experts from North America and Europe - was undertaken in 2018; this allowed us to derive a numerically-formalised pooling of cogent uncertainty judgements.

The results of the SEJ indicated that estimates, particularly for probabilities beyond the likely range used in the AR5 (i.e. 17th-83rd percentile), have grown since the AR5. The SEJ results indicated a 5% probability that global mean sea level could exceed 2 m by 2100, for a business-as-usual temperature scenario, with the ice sheets contributing 178 cm. The study elicited contributions for three processes - ice dynamics, accumulation and runoff - for each of the three ice sheets covering Greenland, West and East Antarctica. Here, we investigate how these three main physical processes influence the long upper tails in the probability density functions for the integrated contributions of each ice sheet.  To interpret the findings, we draw on process-based rationales provided by the experts, which relate ice sheet SLR contributions to ocean and atmospheric forcing and to internal instabilities, and discuss our higher total SLR estimates in relation to earlier studies.

How to cite: Aspinall, W., Cooke, R., Kopp, B., Bamber, J., and Oppenheimer, M.: Interpretation and Analysis of Projected Ice Sheet Contributions from a Structured Expert Judgement, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5747, https://doi.org/10.5194/egusphere-egu2020-5747, 2020.

EGU2020-10792 | Displays | CR1.1

GrSMBMIP: Intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice sheet

Xavier Fettweis and the The GrSMBMIP team

The Greenland Ice Sheet (GrIS) mass loss has been accelerating at a rate of about 20 +/- 10 Gt/yr2 since the end of the 1990's, with around 60% of this mass loss directly attributed to enhanced surface meltwater runoff. However, in the climate and glaciology communities, different approaches exist on how to model the different surface mass balance (SMB) components using: (1) complex physically-based climate models which are computationally expensive; (2) intermediate complexity energy balance models; (3) simple and fast positive degree day models which base their inferences on statistical principles and are computationally highly efficient. Additionally, many of these models compute the SMB components based on different spatial and temporal resolutions, with different forcing fields as well as different ice sheet topographies and extents, making inter-comparison difficult. In the GrIS SMB model intercomparison project (GrSMBMIP) we address these issues by forcing each model with the same data (i.e., the ERA-Interim reanalysis) except for two global models for which this forcing is limited to the oceanic conditions, and at the same time by interpolating all modelled results onto a common ice sheet mask at 1 km horizontal resolution for the common period 1980-2012. The SMB outputs from 13 models are then compared over the GrIS to (1) SMB estimates using a combination of gravimetric remote sensing data from GRACE and measured ice discharge, (2) ice cores, snow pits, in-situ SMB observations, and (3) remotely sensed bare ice extent from MODerate-resolution Imaging Spectroradiometer (MODIS). Our results reveal that the mean GrIS SMB of all 13 models has been positive between 1980 and 2012 with an average of 340 +/- 112 Gt/yr, but has decreased at an average rate of -7.3 Gt/yr2 (with a significance of 96%), mainly driven by an increase of 8.0 Gt/yr2 (with a significance of 98%) in meltwater runoff. Spatially, the largest spread among models can be found around the margins of the ice sheet, highlighting the need for accurate representation of the GrIS ablation zone extent and processes driving the surface melt. In addition, a higher density of in-situ SMB observations is required, especially in the south-east accumulation zone, where the model spread can reach 2 mWE/yr due to large discrepancies in modelled snowfall accumulation. Overall, polar regional climate models (RCMs) perform the best compared to observations, in particular for simulating precipitation patterns. However, other simpler and faster models have biases of same order than RCMs with observations and remain then useful tools for long-term simulations. It is also interesting to note that the ensemble mean of the 13 models produces the best estimate of the present day SMB relative to observations, suggesting that biases are not systematic among models. Finally, results from MAR forced by ERA5 will be added in this intercomparison to evaluate the added value of using this new reanalysis as forcing vs the former ERA-Interim reanalysis (used in SMBMIP). 

How to cite: Fettweis, X. and the The GrSMBMIP team: GrSMBMIP: Intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10792, https://doi.org/10.5194/egusphere-egu2020-10792, 2020.

EGU2020-11667 | Displays | CR1.1

Contrasting contributions to future sea level under CMIP5 and CMIP6 scenarios from the Greenland and Antarctic ice sheets

Tony Payne, Sophie Nowicki, and Heiko Goelzer and the ISMIP6 team

Projections of sea level contribution from the Greenland and Antarctic ice sheets rely on atmospheric and oceanic drivers obtained from climate models.  The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared to the previous CMIP5 effort. Here we use four CMIP6 models and a selection of CMIP5 models under two future climate scenarios to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the multi ice sheet models under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for the Greenland ice sheet.  

How to cite: Payne, T., Nowicki, S., and Goelzer, H. and the ISMIP6 team: Contrasting contributions to future sea level under CMIP5 and CMIP6 scenarios from the Greenland and Antarctic ice sheets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11667, https://doi.org/10.5194/egusphere-egu2020-11667, 2020.

EGU2020-15261 | Displays | CR1.1

Evaluation of a new snow albedo scheme in RACMO2 for the Greenland ice sheet

Christiaan van Dalum, Willem Jan van de Berg, Stef Lhermitte, and Michiel van den Broeke

Snow and ice albedo schemes in present day climate models often lack a sophisticated radiation penetration scheme and are limited to a broadband albedo. In this study, we evaluate a new snow albedo scheme in the regional climate model RACMO2 that uses the two-stream radiative transfer in snow model TARTES and the spectral-to-narrowband albedo module SNOWBAL for the Greenland ice sheet. Additionally, the bare ice albedo parameterization has been updated. The snow and ice albedo output of the updated version of RACMO2, referred to as RACMO2.3p3, is evaluated using PROMICE and K-transect in-situ data and MODIS remote-sensing observations. Generally, the RACMO2.3p3 albedo is in very good agreement with satellite observations, leading to a domain-averaged bias of only -0.012. Some discrepancies are, however, observed for regions close to the ice margin. Compared to the previous iteration RACMO2.3p2, the albedo of RACMO2.3p3 is considerably higher in the bare ice zone during the ablation season, as atmospheric conditions now alter the bare ice albedo. For most other regions, however, the albedo of RACMO2.3p3 is lower due to spectral effects, radiation penetration, snow metamorphism or a delayed firn-ice transition. Furthermore, a white-out effect during cloudy conditions is captured and the snow albedo shows a low sensitivity to low soot concentrations. The surface mass balance of RACMO2.3p3 compares well with observations. Subsurface heating, however, now leads to increased melt and refreezing in south Greenland, changing the snow structure.

How to cite: van Dalum, C., van de Berg, W. J., Lhermitte, S., and van den Broeke, M.: Evaluation of a new snow albedo scheme in RACMO2 for the Greenland ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15261, https://doi.org/10.5194/egusphere-egu2020-15261, 2020.

Global warming has become a world concerned issue which draws increasingly attention of the scientific community. Sea-level rise is an important indicator of Global warming as it integrates many factors of climate change including ice sheet melting.  The accurate assessment of the Antarctic ice sheet mass balance is applied to deeply explore the impact of minor change in Antarctic ice sheet on sea level rise. Based on multi-source remote sensing product, we finely estimated the mass balance of the Antarctic ice sheet and discussed dynamics and climatological causes of the fluctuations from 2005 to 2015 by IOM (Input-Output-Method).

In our study, the calculation method of ice flux on the grounding line is improved. We also precisely evaluate the ice flux as an output component. The result shows that: (1) The Antarctic ice sheet was continuously losing mass during the period of 2005-2016. (2) The mass loss of the Antarctic ice sheet was dominated by West Antarctica when East Antarctica was in a positive mass balance, but some basins also occurred significant mass loss. The Antarctic peninsula fluctuated in a state of zero balance. (3) The change in the mass balance of the ice sheet was dominated by the surface mass balance as a whole, and was mainly affected by the interannual variation of climatological factors. From a small-scale perspective, ice shelf thinning and glacier calving causes the change of ice flux on the grounding line. That change leads to the severe mass loss in the region it happened. Therefore the mass loss in the year of the disintegration event happened increases.

How to cite: Lin, Y.: Antarctic Ice Sheet mass balance over the past decade from 2005 to 2016 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12835, https://doi.org/10.5194/egusphere-egu2020-12835, 2020.

EGU2020-7865 | Displays | CR1.1

Greenland Ice Sheet surface runoff projections to AD2500 using degree-day model

Chao Yue, Liyun Zhao, and John C. Moore

      The Greenland ice sheet (GrIS) surface melt-water runoff dominates recent ice mass loss under global warming. We present runoff simulations during 1950-2500 over GrIS under RCP (Representative Concentration Pathways) 4.5, RCP8.5 and their extensions scenarios using three modified degree-day models, forced with five CMIP5 (Coupled Model Intercomparison Project) Earth System Models (CanESM2, BNU-ESM, HadGEM2-ES, MIROC-ESM and MIROC-ESM-CHEM). The degree-day factors are tuned at two sites on Greenland to best match the results by surface energy and mass balance model SEMIC. The modeled SMB over Greenland by modified degree-day models agree well with SEMIC in 21th century, then is applied to do projections for the 2100-2500 period. We also consider equilibrium line altitude evolution, surface topography changes and runoff-elevation feedback in the post-2100 simulations. The ensemble mean projected GrIS runoff is equivalent to sea-level rise of 7 cm (RCP4.5) and 10 cm (RCP8.5) by the end of the 21st century relative to the period 1950-2005, and 25cm (RCP4.5) and 121cm (RCP8.5) by 2500. Runoff-elevation feedback increases extra runoff of 7% (RCP4.5, RCP8.5) by 2100 and 23% (RCP4.5) and 22% (RCP8.5) by 2500. Sensitivity experiments show that 150% and 200% snowfall in post-2100 period would lead to 10% and 20% runoff increase under RCP4.5, 5% and 10% for RCP8.5, respectively.

How to cite: Yue, C., Zhao, L., and Moore, J. C.: Greenland Ice Sheet surface runoff projections to AD2500 using degree-day model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7865, https://doi.org/10.5194/egusphere-egu2020-7865, 2020.

Interannual variations associated with El Niño-Southern Oscillation can alter the surface-pressure distribution and moisture transport over Antarctica, potentially affecting the contribution of the Antarctic ice sheet to sea level. Here, we combine satellite gravimetry with auxiliary atmospheric datasets to investigate interannual ice-mass changes during the extreme 2015-16 El Niño. Enhanced precipitation during this event contributed positively to the mass of the Antarctic Peninsula and West Antarctic ice sheets, with the mass gain on the peninsula being unprecedented within GRACE’s observational record. Over the coastal basins of East Antarctica, the precipitation-driven mass loss observed in recent years was arrested, with pronounced accumulation over Terre Adélie dominating this response. Little change was observed over Central Antarctica where, after a brief pause, enhanced mass-loss due to weakened precipitation continued. Overall, precipitation changes over this period were sufficient to temporarily offset Antarctica’s usual (approximately 0.4 mm yr-1) contribution to global mean sea level rise.

How to cite: Bingham, R. and Bodart, J.: The Impact of the Extreme 2015-16 El Niño on the Mass Balance of the Antarctic Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2900, https://doi.org/10.5194/egusphere-egu2020-2900, 2020.

EGU2020-19032 | Displays | CR1.1

A regional atmospheric warming threshold for irreversible Greenland ice sheet mass loss

Michiel van den Broeke, Brice Noël, Leo van Kampenhout, and Willem-Jan van de Berg

The mass balance of the Greenland ice sheet (GrIS, units Gt per year) equals the surface mass balance (SMB) minus solid ice discharge across the grounding line. As the latter is definite positive, an important threshold for irreversible GrIS mass loss occurs when long-term average SMB becomes negative. For this to happen, runoff (mainly meltwater, some rain) must exceed mass accumulation (mainly snowfall minus sublimation). Even for a single year, this threshold has not been passed since at least 1958, the first year with reliable estimates of SMB components, although recent years with warm summers (e.g. 2012 and 2019) came close. Simply extrapolating the recent (1991-present) negative SMB trend into the future suggests that the SMB = 0 threshold could be reached before ~2040, but such predictions are extremely uncertain given the very large interannual SMB variability, the relative brevity of the time series and the uncertainty in future warming. In this study we use a cascade of models, extensively evaluated with in-situ and remotely sensed (GRACE) SMB observations, to better constrain the future regional warming threshold for the 5-year average GrIS SMB to become negative. To this end, a 1950-2100 climate change run with the global model CESM2 (app. 100 km resolution) was dynamically downscaled using the regional climate model RACMO2 (app. 11 km), which in turn was statistically downscaled to 1 km resolution. The result is a threshold regional Greenland warming of close to 4 degrees. We then use a range of CMIP5 and CMIP6 global climate models to translate the regional value into a global warming threshold for various warming scenarios, including its timing this century. We find substantial differences, ranging from stabilization before the threshold is reached in the RCP/SSP2.6 scenarios with a limited but still significant sea-level rise contribution (< 5 cm by 2100) to an imminent crossing of the warming threshold for the RCP/SSP8.5 scenarios with substantial and ever-growing contributions to sea level rise (> 10 cm by 2100). These results stress the need for strong mitigation to avoid irreversible GrIS mass loss. We finish by discussing the caveats and uncertainties of our approach.

How to cite: van den Broeke, M., Noël, B., van Kampenhout, L., and van de Berg, W.-J.: A regional atmospheric warming threshold for irreversible Greenland ice sheet mass loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19032, https://doi.org/10.5194/egusphere-egu2020-19032, 2020.

EGU2020-10941 | Displays | CR1.1

Tipping Points in Antarctic Climate Components (TiPACCs)

Petra Langebroek, Svein Østerhus, and TiPACCs Consortium

Recently, several of the West Antarctic ice shelves have experienced thinning driven by ocean-induced basal melting. The consequent reduction in buttressing of the Antarctic ice sheet causes an increase in the discharge of the grounded ice into the ocean.

In our new Horizon 2020 project “Tipping Points in Antarctic Climate Components” (TiPACCs) we address these processes by assessing the possible switch from “cold” to “warm” Antarctic continental shelf seas (tipping point 1) and the possible shift in the stability regime of the Antarctic ice sheet from a stable to an unstable configuration (tipping point 2). Investigating the coupled ocean-ice system, the tipping points and their feedbacks, will provide insight into the threat of abrupt and large sea-level rise. In TiPACCs we use a suite of state-of-the-art ocean circulation and ice sheet models, in stand-alone and coupled set-up. The proximity of the simulated tipping points will be determined by existing remote sensing and in-situ observations. The possibility that the tipping points were crossed during the Last Interglacial will be investigated and allow for a better understanding of how the ocean-ice system works during warmer than present-day conditions.

This EGU contribution will present the ideas, the planned work, and the consortium of TiPACCs.

How to cite: Langebroek, P., Østerhus, S., and Consortium, T.: Tipping Points in Antarctic Climate Components (TiPACCs), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10941, https://doi.org/10.5194/egusphere-egu2020-10941, 2020.

EGU2020-19502 | Displays | CR1.1

Doubling of future Greenland Ice Sheet surface melt revealed by the new CMIP6 high-emission scenario

Stefan Hofer, Charlotte Lang, Charles Amory, Christoph Kittel, Alison Delhasse, Andrew Tedstone, Patrick Alexander, Robin Smith, and Xavier Fettweis

Future climate projections show a marked increase in Greenland Ice Sheet (GrIS) runoff
during the 21st century, a direct consequence of the Polar Amplification signal. Regional
climate models (RCMs) are a widely used tool to downscale ensembles of projections from
global climate models (GCMs) to assess the impact of global warming on GrIS melt and
sea level rise contribution. Initial results of the CMIP6 GCM model intercomparison
project have revealed a greater 21st century temperature rise than in CMIP5 models.
However, so far very little is known about the subsequent impacts on the future GrIS
surface melt and therefore sea level rise contribution. Here, we show that the total GrIS
melt during the 21st century almost doubles when using CMIP6 forcing compared to the
previous CMIP5 model ensemble, despite an equal global radiative forcing of +8.5 W/m2
in 2100 in both RCP8.5 and SSP58.5 scenarios. The total GrIS sea level rise contribution
from surface melt in our high-resolution (15 km) projections is 17.8 cm in SSP58.5, 7.9 cm
more than in our RCP8.5 simulations, despite the same radiative forcing. We identify a
+1.7°C greater Arctic amplification in the CMIP6 ensemble as the main driver behind the
presented doubling of future GrIS sea level rise contribution

How to cite: Hofer, S., Lang, C., Amory, C., Kittel, C., Delhasse, A., Tedstone, A., Alexander, P., Smith, R., and Fettweis, X.: Doubling of future Greenland Ice Sheet surface melt revealed by the new CMIP6 high-emission scenario, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19502, https://doi.org/10.5194/egusphere-egu2020-19502, 2020.

EGU2020-6309 | Displays | CR1.1

ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century

Helene Seroussi, Heiko Goelzer, and Mathieu Morlighem and the ISMIP6 Team

Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to differ- ent climate scenarios and inform on the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimated the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes and the forcings employed. This study presents results from 18 simulations from 15 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015-2100, forced with different scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5) representative of the spread in climate model results. The contribution of the Antarctic ice sheet in response to increased warming during this period varies between -7.8 and 30.0 cm of Sea Level Equivalent (SLE). The evolution of the West Antarctic Ice Sheet varies widely among models, with an overall mass loss up to 21.0 cm SLE in response to changes in oceanic conditions. East Antarctica mass change varies between -6.5 and 16.5 cm SLE, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional mass loss of 8 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 AOGCMs show an overall mass loss of 10 mm SLE compared to simulations done under present-day conditions, with limited mass gain in East Antarctica.

How to cite: Seroussi, H., Goelzer, H., and Morlighem, M. and the ISMIP6 Team: ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6309, https://doi.org/10.5194/egusphere-egu2020-6309, 2020.

EGU2020-18721 | Displays | CR1.1

How will the Greenland Ice Sheet develop under Extreme Melt Events?

Johanna Beckmann, Alison Delhasse, and Ricarda Winkelmann

 

How to cite: Beckmann, J., Delhasse, A., and Winkelmann, R.: How will the Greenland Ice Sheet develop under Extreme Melt Events?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18721, https://doi.org/10.5194/egusphere-egu2020-18721, 2020.

EGU2020-9208 | Displays | CR1.1

Changes on Totten glacier dependent on oceanic forcing based on ISMIP6

Konstanze Haubner, Sainan Sun, Lars Zipf, and Frank Pattyn

Totten glacier is draining 68% of the Aurora basin, East Antarctica, - an equivalent to 3.5m global sea level rise. Further, Totten’s thickness and velocity have been fluctuating during the last decades showing periodic speed-ups and thinning.

We investigate the effect of different ocean forcing on Totten glacier using the state-of-the-art ice sheet model BISICLES and based on the high-resolution data sets BedMachine Antarctica and REMA (Morlighem et al., 2019; Howat et al., 2019). Our simulations (2015-2100) are following the ISMIP6 setup and are based on CMIP5 & CMIP6 AOGCM outputs under RCP8.5 and RCP2.6. The contribution to sea level at 2100 varies between plus and minus 6mm. For all scenarios, we see thinning at the sides of Totten glacier in the slower flowing areas, but only climate models with sub-shelf melt rates that are at least 8m/a above the reference melt rates (1995 – 2017) lead to thinning and acceleration across Totten's grounding line. In agreement with ISMIP6 results, non-local quadratic melt rates adjusted to present day conditions at Pine island glacier, West Antarctica, results in the highest sub-shelf melt rates for all AOGCMs (up to 80m/a locally).

The ISMIP6 ocean melt scheme is based on a feedback given the simulated ice draft change: the thermal forcing of the ocean model is taken from the ocean layer closest to the bottom of the ice shelf at the current simulation step. Simulations not including this feedback lead to higher mass loss than the standard ISMIP6 scenario including the feedback.

How to cite: Haubner, K., Sun, S., Zipf, L., and Pattyn, F.: Changes on Totten glacier dependent on oceanic forcing based on ISMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9208, https://doi.org/10.5194/egusphere-egu2020-9208, 2020.

Projections of the contribution of the Greenland ice sheet to future sea-level rise include uncertainties primarily due to the imposed climate forcing and the initial state of the ice sheet model. Several state-of-the-art ice flow models are currently being employed on various grid resolutions to estimate future mass changes in the framework of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Here we investigate the sensitivity to grid resolution on centennial sea-level contributions from the Greenland ice sheet and study the mechanism at play. To this end, we employ the finite-element higher-order ice flow model ISSM and conduct experiments with four different horizontal resolutions, namely 4, 2, 1 and 0.75 km. We run the simulation based on the ISMIP6 core GCM MIROC5 under the high emission scenario RCP8.5 and consider both atmospheric and oceanic forcing in full and separate scenarios. Under the full scenarios, finer simulations unveil up to 5% more sea-level rise compared to the coarser resolution. The sensitivity depends on the magnitude of outlet glacier retreat, which is implemented as a series of retreat masks following the ISMIP6 protocol. Without imposed retreat under atmosphere-only forcing, the resolution dependency exhibits an opposite behaviour with about 5% more sea-level contribution in the coarser resolution. The sea-level contribution indicates a converging behaviour ≤ 1 km horizontal resolution. A driving mechanism for differences is the ability to resolve the bed topography, which highly controls ice discharge to the ocean. Additionally, thinning and acceleration emerge to propagate further inland in high resolution for many glaciers. A major response mechanism is sliding (despite no climate-induced hydrological feedback is invoked), with an enhanced feedback on the effective normal pressure N at higher resolution leading to a larger increase in sliding speeds under scenarios with outlet glacier retreat.

How to cite: Rückamp, M., Goelzer, H., Kleiner, T., and Humbert, A.: Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14565, https://doi.org/10.5194/egusphere-egu2020-14565, 2020.

Earth System Models (ESMs) are composed of different components, including submodels as well as whole domain models. Within such an ESM, these model components need to exchange information to account for the interactions between the different compartments. This exchange of data is the purpose of a “model coupler”.

Within the Advanced Earth System Modelling Capacity (ESM) project, a goal is to develop a modular framework that allows for a flexible ESM configuration. One approach is to implement purpose build model couplers in a more modular way.

For this purpose, we developed the esm-interface library, in consideration of the following objectives: (i) To obtain a more modular ESM, that allows model components and model couplers to be exchangeable; and (ii) to account for a more flexible coupling configuration of an ESM setup.

As a first application of the esm-interface library, we implemented it into the AWI Climate Model (AWI-CM) [Sidorenko et al., 2015] as an interface between the model components and the model coupler (OASIS3-MCT; Valcke [2013]). In a second step, we extended the esm-interface library for a second coupler (YAC; Hanke et al. [2016]).

In this presentation, we will discuss the general idea of the esm-interface library, it’s implementation in an ESM setup and show first results from the first modular prototype of AWI-CM.

How to cite: Wieters, N., Barbi, D., and Cristini, L.: Modular AWI-CM: An Earth System Model (ESM) prototype using the esm-interface library for a modular ESM coupling approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6990, https://doi.org/10.5194/egusphere-egu2020-6990, 2020.

EGU2020-16948 | Displays | CR1.1

ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model

Thomas Kleiner, Jeremie Schmiedel, and Angelika Humbert

Ice sheets constitute the largest and most uncertain potential source of future sea-level rise. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice sheet and climate models to explore the contribution from the Greenland and Antarctic ice sheets to future sea-level rise.

We use the Parallel Ice Sheet Model (PISM, pism-docs.org) to carry out spinup and projection simulations for the Antarctic Ice Sheet. Our treatment of the ice-ocean boundary condition previously based on 3D ocean temperatures (initMIP-Antarctica) has been adopted to use the ISMIP6 parameterisation and 3D ocean forcing fields (temperature and salinity) according to the ISMIP6 protocol.

In this study, we analyse the impact of the choices made during the model initialisation procedure on the initial state. We present the AWI PISM results of the ISMIP6 projection simulations and investigate the ice sheet response for individual basins. In the analysis, we distinguish between the local and non-local ice shelf basal melt parameterisation.

How to cite: Kleiner, T., Schmiedel, J., and Humbert, A.: ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16948, https://doi.org/10.5194/egusphere-egu2020-16948, 2020.

CR1.2 – The Antarctic Ice Sheet: past, present and future contributions towards global sea level

Sea-level rise is among the greatest risks that arise from anthropogenic global climate change. It is receiving a lot of attention, among others in the IPCC reports, but major questions remain as to the potential contribution from the great continental ice sheets. In recent years, some modelling work has suggested that the ice-component of sea-level rise may be much faster than previously thought, but the rapidity of rise seen in these results depends on inclusion of scientifically debated mechanisms of ice-shelf decay and associated ice-sheet instability. The processes have not been active during historical times, so data are needed from previous warm periods to evaluate whether the suggested rates of sea-level rise are supported by observations or not. Also, we then need to assess which of the ice sheets was most sensitive, and why. The last interglacial (LIG; ~130,000 to ~118,000 years ago, ka) was the last time global sea level rose well above its present level, reaching a highstand of +6 to +9 m or more. Because Greenland Ice Sheet (GrIS) contributions were smaller than that, this implies substantial Antarctic Ice Sheet (AIS) contributions. However, this still leaves the timings, magnitudes, and drivers of GrIS and AIS reductions open to debate. I will discuss recently published sea-level reconstructions for the LIG highstand, which reveal that AIS and GrIS contributions were distinctly asynchronous, and that rates of rise to values above 0 m (present-day sea level) reached up to 3.5 m per century. Such high pre-anthropogenic rates of sea-level rise lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations, for both the past and future. Climate forcing was distinctly asynchronous between the southern and northern hemispheres as well during the LIG, explaining the asynchronous sea-level contributions from AIS and GrIS. Today, climate forcing is synchronous between the two hemispheres, and also faster and greater than during the LIG. Therefore, LIG rates of sea-level rise should likely be considered minimum estimates for the future.

How to cite: Rohling, E. and Hibbert, F.: Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1513, https://doi.org/10.5194/egusphere-egu2020-1513, 2020.

EGU2020-3099 | Displays | CR1.2

The contribution of the East Antarctic Ice Sheet to future sea level rise

Jim Jordan, Hilmar Gudmundsson, Adrian Jenkins, Chris Stokes, Stewart Jamieson, and Bertie Miles

The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing a water mass equivalent of 53 m. Recent work has found the overall mass balance of the EAIS to be approximately in equilibrium, albeit with large uncertainties. However, changes in oceanic conditions have the potential to upset this balance. This could happen by both a general warming of the ocean and also by shifts in oceanic conditions allowing warmer water masses to intrude into ice shelf cavities.

We use the Úa numerical ice-flow model, combined with ocean-melt rates parameterized by the PICO box mode, to predict the future contribution to global-mean sea level of the EAIS. Results are shown for the next 100 years under a range of emission scenarios and oceanic conditions on a region by region basis, as well as for the whole of the EAIS. 

How to cite: Jordan, J., Gudmundsson, H., Jenkins, A., Stokes, C., Jamieson, S., and Miles, B.: The contribution of the East Antarctic Ice Sheet to future sea level rise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3099, https://doi.org/10.5194/egusphere-egu2020-3099, 2020.

EGU2020-14352 | Displays | CR1.2

The uncertainty in Antarctic sea-level rise projections due to ice dynamics

Javier Blasco, Ilaria Tabone, Daniel Moreno, Jorge Alvarez-Solas, Alexander Robinson, and Marisa Montoya

Projections of the Antarctic Ice Sheet (AIS) contribution to future global sea-level rise are highly uncertain, partly due to the potential threat of a collapse of the marine sectors of the AIS. However, whether the inherent instability of such sectors is already underway or is still far away from being triggered remains elusive. One reason for ambiguity in results relies on the uncertainty of basal conditions. Whereas high basal friction can potentially prevent a collapse of the marine zones of the AIS, low basal friction can promote such a process. In addition, future sea-level projections from the AIS are generally run from an equilibrated present-day (PD) state tuned to observational data. However, this procedure neglects the thermal memory of the ice sheet. Furthermore, there is no apparent reason for ruling out that the PD may be subject to a natural drift since the onset of the last deglaciation (~20 kyr BP). Here we study the uncertainty in sea-level projections by investigating the response of the AIS to different RCP scenarios for four different basal-dragging laws. For this purpose we use a three-dimensional ice-sheet-shelf model that is spun up from a deglaciation. Model parameters of all friction laws have been optimized to simulate a realistic PD. In addition, we study the response of the AIS to a sudden CO2 drop to investigate the potential irreversibility of the ice sheet depending on the RCP scenario and friction law.

How to cite: Blasco, J., Tabone, I., Moreno, D., Alvarez-Solas, J., Robinson, A., and Montoya, M.: The uncertainty in Antarctic sea-level rise projections due to ice dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14352, https://doi.org/10.5194/egusphere-egu2020-14352, 2020.

EGU2020-16045 | Displays | CR1.2

Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne Ice Shelf System

Emily Hill, Sebastian Rosier, Hilmar Gudmundsson, and Matthew Collins

Mass loss from the Antarctic Ice Sheet is the main source of uncertainty in projections of future sea-level rise, with important implications for coastal regions worldwide. Enhanced melt beneath ice shelves could destabilise large parts of the ice sheet, and further increase ice loss. Despite advances in our understanding of feedbacks in the ice sheet-ice shelf-ocean system, future projections of ice loss remain poorly constrained in many parts of Antarctica. In particular, there is ongoing debate surrounding the future of the Filchner-Ronne Ice Shelf (FRIS) region. The FRIS has remained relatively unchanged in recent decades, but an increase in air and ocean temperatures in the neighbouring Weddell Sea, could force rapid retreat in the near future. Indeed, previous modelling work has suggested the potential for widespread infiltration of warm water beneath the ice shelf in the second half of the twenty-first century, leading to a drastic increase in basal melting.

Here, we use the ice flow model Úa alongside the ocean box model PICO (Potsdam Ice-shelf Cavity mOdel) to understand the key physical processes and model variability in future projections of sea level rise from the FRIS region. We investigate uncertain model parameters associated with ice dynamics, surface melting and precipitation, ocean temperature forcing, and parameters relating to the strength of basal melt generated by PICO. We optimise the prior distributions of parameters in PICO using observations and a Bayesian approach, leading to improved posterior distributions for use in the following stages of uncertainty quantification. We then run our forward model through the 21st century for various RCP scenarios and extensive random sampling of uncertain parameters to train an emulator. From this, we present probabilistic projections of potential sea level rise from the FRIS region for different future climate change scenarios, together with a sensitivity analysis to identify the most important parameters that contribute to uncertainty in these projections.

How to cite: Hill, E., Rosier, S., Gudmundsson, H., and Collins, M.: Quantifying uncertainty in future projections of ice loss from the Filchner-Ronne Ice Shelf System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16045, https://doi.org/10.5194/egusphere-egu2020-16045, 2020.

EGU2020-4196 | Displays | CR1.2

The impact of internal variability in ocean-induced melting on Totten Glacier

Felicity McCormack, Mathieu Morlighem, David Gwyther, Jason Roberts, and Tyler Pelle

The Totten Glacier, located in the Aurora Subglacial Basin of East Antarctica, drains a catchment containing approximately 3.5 m of global sea level rise equivalent ice mass. The This glacier has been losing mass over recent decades, and modelling studies indicate that it is the most vulnerable glacier in East Antarctica to warming oceans and atmosphere over the coming century. Satellite altimetry shows high internal variability in ocean-forced melting of the Totten Ice Shelf; however, the extent to which this variability signal impacts the upstream ice sheet dynamics, and therefore its mass balance, is unknown. Here we use the Ice Sheet System Model (ISSM) combined with a plume and basal melting parameterisation called PICOP to investigate the impact of variability in ocean temperature on the evolution of Totten Glacier. We find that the southernmost portion of the Totten Glacier grounding line - from which the majority of the catchment’s ice is channeled - is stable within only a limited range of background ocean temperatures close to present-day values. In the stable simulations, the magnitude of the ice mass flux depends on the extent to which the ice shelf is pinned on a bed topography rumple located approximately 10 km downstream of its grounding line, but the period of the mass flux is decadal to multi-decadal in each simulation, irrespective of the magnitude of the variability in ocean forcing. We further find that the impact of variability in ocean melt rates decreases as the mean background ocean temperature increases, suggesting that the mean state may have a relatively more important role in the evolution of the Totten Glacier than variability in ocean forcing. Our results have implications for detection and attribution of climate change and internal climate variability in modeling studies, and may inform fieldwork campaigns mapping bed topography in the Aurora Subglacial Basin.

How to cite: McCormack, F., Morlighem, M., Gwyther, D., Roberts, J., and Pelle, T.: The impact of internal variability in ocean-induced melting on Totten Glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4196, https://doi.org/10.5194/egusphere-egu2020-4196, 2020.

The distribution of relict moraines in the Transantarctic Mountains affords geologic constraint of past ice-marginal positions of the East Antarctic Ice Sheet (EAIS). We describe the directly dated glacial-geologic record from Roberts Massif, an ice-free area in the central Transantarctic Mountains, to provide a comprehensive record of ice sheet change at this site since the Miocene and to capture ice sheet response to warmer-than-present climate conditions. The record is constrained by cosmogenic 3He, 10Be, 21Ne, and 26Al surface-exposure ages from > 160 dolerite and sandstone erratics on well-preserved moraines and drift units. Our data set indicates that a cold-based EAIS was present, and similar to its current configuration, for long periods over the last ~14.5 Myr, including the mid-Miocene, Late Pliocene, and early-to-mid Pleistocene, with moraine ages increasing with distance from and elevation above the modern ice margin. We also report extremely low erosion rates over the duration of our record, reflecting long-term polar desert conditions at Roberts Massif. The age-elevation distribution of moraines at Roberts Massif is consistent with a persistent EAIS extent during glacial maxima, accompanied by slow, isostatic uplift of the massif due to subglacial erosion. Although our data are not a direct measure of ice volume, the Roberts Massif glacial record indicates that the EAIS was present and of similar extent to today during periods when global temperature was believed to be warmer and/or atmospheric CO2 concentrations were likely higher than today.

How to cite: Bromley, G., Balter, A., Balco, G., and Jackson, M.: A 14.5 million-year geologic record of East Antarctic Ice Sheet fluctuations in the central Transantarctic Mountains, constrained with multiple cosmogenic nuclides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19999, https://doi.org/10.5194/egusphere-egu2020-19999, 2020.

EGU2020-12771 | Displays | CR1.2

Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

Christian Turney, Christopher Fogwill, and Nicholas Golledge and the The AntarcticScience.com Team

The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG; 129-116 kyr), which experienced warmer polar temperatures and higher global mean sea level (GMSL +6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (~2 m), ocean thermal expansion and melting mountain glaciers (~1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic Meridional Overturning Circulation in response to North Atlantic surface freshening.  Here we report a blue-ice record of ice-sheet and environmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS) which is underlain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide the first evidence for substantial mass loss across the Weddell Sea Embayment during the Last Interglacial, most likely driven by ocean warming and associated with destabilization of sub-glacial hydrates. Ice-sheet modelling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multi-meter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice-climate feedbacks that further amplify warming.

How to cite: Turney, C., Fogwill, C., and Golledge, N. and the The AntarcticScience.com Team: Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12771, https://doi.org/10.5194/egusphere-egu2020-12771, 2020.

EGU2020-2456 | Displays | CR1.2

Aurora Basin, the weak underbelly of East Antarctica
not presented

Tyler Pelle, Mathieu Morlighem, and Felicity S. McCormack

Containing ~52 m sea level rise equivalent ice mass (SLRe), the East Antarctic Ice Sheet (EAIS) is a major component of the global sea level budget; yet, uncertainty remains in how this ice sheet will respond to enhanced atmospheric and oceanic thermal forcing through the turn of the century. To address this uncertainty, we model the most dynamic catchments of EAIS out to 2100 using the Ice Sheet System Model. We employ three basal melt rate parameterizations to resolve ice-ocean interactions and force our model with anomalies in both surface mass balance and ocean thermal forcing from both CMIP5 and CMIP6 model output. We find that this sector of EAIS gains approximately 10 mm SLRe by 2100 under high emission scenarios (RCP8.5 and SSP585), and loses mass under low emission scenarios (RCP2.6). All basins within the domain either gain mass or are in near mass balance through the 86-year experimental period, except the Aurora Subglacial Basin. The primary region of mass loss in this basin is located within 50 km upstream of Totten Glacier’s grounding line, which loses up to 6 mm SLRe by 2100. Glacial discharge from Totten is modulated by buttress supplied by a 10 km ice plain, located along the southern-most end of Totten’s grounding line. This ice plain is sensitive to brief changes in ocean temperature and once ungrounded, glacial discharge from Totten accelerates by up to 70% of it present day configuration. In all, we present plausible bounds on the contribution of a large sector of EAIS to global sea level rise out to the end of the century and target Totten as the most vulnerable glacier in this region. In doing so, we reduce uncertainty in century-scale global sea level projections and help steer scientific focus to the most dynamic regions of EAIS.

How to cite: Pelle, T., Morlighem, M., and S. McCormack, F.: Aurora Basin, the weak underbelly of East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2456, https://doi.org/10.5194/egusphere-egu2020-2456, 2020.

The fast ice in the McMurdo Sound plays an important role in the coastal ecological systems and climate changes, but its seasonal and interannual variations are poorly understood. In this study, the fast ice phenology and extent variation are investigated using Sentinel-1 Synthetic Aperture Radar (SAR) images from 2017 to 2019, and the factors controlling the fast ice development are explored. The results showed that the fast ice edge presented obvious seasonal change. In 2017/2018 and 2018/2019 years it arrived at northernmost during May – July, and keeps north until the end of December or January, and then moves south, arriving at most south on February or March. However, there are some difference between these two years. The date the fast ice edge arrived at northernmost in 2018 was about two months later than in 2017, but the ending time at the northern edge was about one month earlier (31 Dec 2018 vs 30 Jan 2018). The time when it retreated to the southernmost in 2019 was about one month before that in 2017 or 2018. It seems the longer the edge stays in the northernmost, the later it retreats to the southernmost, and it may not completely disappear; the shorter the edge stays in the northernmost, the earlier it retreats to the southernmost, and it may completely disappear. The dominant factor controlling the beginning and end dates are air temperature. This statement still needs to be confirmed when more data will be processed and analyzed in near future.

How to cite: Dai, L.:  Seasonal variability of fast ice edge in the McMurdo Sound between 2017 and 2019 based on Sentinel-1 SAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2857, https://doi.org/10.5194/egusphere-egu2020-2857, 2020.

EGU2020-6572 | Displays | CR1.2

Estimating Antarctic Ice Sheet Contributions to Future Sea Level Rise Using a Coupled Climate-Ice Sheet Model

Jun-Young Park, Fabian Schloesser, Axel Timmermann, Dipayan Choudhury, June-Yi Lee, Arjun Babu Nellikkattil, and David Pollard

One of the largest uncertainties in projecting future global mean sea level (GSML) rise in response to anthropogenic global warming originates from the Antarctic ice sheet (AIS) contribution. Previous studies suggested that a potential AIS collapse due to the Marine Ice Sheet Instability (MISI) and Marine Ice Cliff Instability (MICI) may contribute up to 1m GMSL rise by the year 2100. However, these estimates were based on uncoupled ice sheet models that do not capture interactions between the AIS and the ocean and atmosphere. Here, we explore future GMSL projections using a three-dimensional coupled climate-ice sheet model (LOVECLIP) that simulates ice sheet dynamics in both hemispheres. The model was forced by increasing CO2 concentrations following the Shared Socioeconomic Pathway (SSP) 1-1.9, 2-4.5 and 5-8.5 scenarios. Over the next 80 years, the corresponding GMSL contribution from AIS amounts to about 2cm, 8cm and 11cm, respectively. Additional sensitivity experiments show that AIS meltwater flux in response to the SSP 5-8.5 CO2 concentrations causes subsurface Southern Ocean warming which leads to an additional 20% AIS melting and a reduction in Southern Hemispheric future warming.

How to cite: Park, J.-Y., Schloesser, F., Timmermann, A., Choudhury, D., Lee, J.-Y., Nellikkattil, A. B., and Pollard, D.: Estimating Antarctic Ice Sheet Contributions to Future Sea Level Rise Using a Coupled Climate-Ice Sheet Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6572, https://doi.org/10.5194/egusphere-egu2020-6572, 2020.

EGU2020-11191 | Displays | CR1.2

Obliquity pacing of Antarctic glaciations during the Quaternary

Christian Ohneiser, Catherine Beltran, Christina Hulbe, Chris Moy, Christina Riesselman, Rachel Worthington, and Donna Condon

Obliquity pacing of Antarctic glaciations during the Quaternary

The frequency of Antarctic glaciations during the Quaternary are not well understood. Benthic oxygen isotope records provide evidence for eccentricity paced global ice volume changes since c. 800 000 years and the ice core records (such as EPICA) also appear to have 100 000 year cycles over the last 800 000 years. However, the benthic oxygen isotope records are a global average – not an Antarctic record. Quaternary, sedimentary records proximal to the ice margin (such as the ANDRILL AND-1B record) are needed to understand better the recent glacial history of Antarctica. 

Here we present results from the 6.21 m long, NBP03-01A-20PCA sedimentary record which was recovered from the outer continental margin of the Ross Embayment.

Sediments comprise mud with numerous clasts and paleomagnetic analyses revealed magnetic reversals at 4.21 m, 5.74 m, and 5.85 m depth. These reversals are correlated with C1n-C1r.1r-C1r.1n-C1r.2r geomagnetic reversals which have corresponding ages of 773 ka, 990 ka, and 1070 ka. 

Time series analysis of continuous Anhysteretic Remanent Magnetisation (ARM) data, which are controlled primarily by the concentration of magnetic minerals, revealed strong obliquity paced cycles between c. 800 ka and 350 ka. The presence of obliquity cycles prompted us to carry out core scanning XRF and grain size analyses. The archive half was scanned in a itrax XRF core scanner at the Marine and Geology Repository at Oregon State University and high density grain size analyses were conducted at the University of Otago. 

We identified obliquity paced cycles in the titanium elemental data over the same period which we suggest represent variations in the terrigenous material in the core. Weaker obliquity cycles are also present in the >2mm grain size fraction which we suggest is controlled by the proximity of the ice shelf front. 

We suggest that the presence of obliquity paced cycles in our data series indicate that the Ross Ice Shelf calving line advance and retreat cycles were paced with obliquity until at least 350 ka and that the mid-Pleistocene transition occurred later in the Southern Hemisphere than in the North. 

How to cite: Ohneiser, C., Beltran, C., Hulbe, C., Moy, C., Riesselman, C., Worthington, R., and Condon, D.: Obliquity pacing of Antarctic glaciations during the Quaternary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11191, https://doi.org/10.5194/egusphere-egu2020-11191, 2020.

EGU2020-12028 | Displays | CR1.2

Rapid Antarctic ice sheet retreat under low atmospheric CO2

Catherine Beltran, Nicholas R. Golledge, Christian Ohneiser, Douglas E. Kowalewski, Marie-Alexandrine Sicre, Kimberly J. Hageman, Robert O. Smith, Gary S. Wilson, and François Mainié

Over the last 5 Million years, outstanding warm interglacial periods (i.e. ‘super-interglacials’) occurred under low atmospheric CO2 levels that may feature extensive Antarctica ice sheet collapse. Here, we focus on the extreme super-interglacial known as Marine Isotope Stage 31 (MIS31) that took place 1.072 million years ago and is the subject of intense debate.

Our Southern Ocean organic biomarker based paleotemperature reconstructions show that the surface ocean was warmer by ~5 °C than today between 50 °S and the Antarctic ice margin. We used these ocean temperature records to constrain the climate and ice sheet simulations to explore the impact of ocean warming on the Antarctic ice sheets. Our results show that low amplitude short term oceanic modifications drove the collapse of the West Antarctic Ice Sheet (WAIS) and deflation of sectors of the East Antarctic Ice Sheet (EAIS) resulting in sustained sea-level rise of centimeters to decimeters per decade.

We suggest the WAIS retreated because of anomalously high Southern Hemisphere insolation combined with the intrusion of Circumpolar Deep Water onto the continental shelf under poleward-intensified winds leading to a shorter sea ice season and ocean warming at the continental margin. Under this scenario, the extreme warming we observe likely reflects the extensively modified oceanic and hydrological circulation patterns following ice sheet collapse. Our work highlights the sensitivity of the Antarctic ice sheets to relatively minor oceanic and/or atmospheric perturbations that could be at play in the near future.

How to cite: Beltran, C., Golledge, N. R., Ohneiser, C., Kowalewski, D. E., Sicre, M.-A., Hageman, K. J., Smith, R. O., Wilson, G. S., and Mainié, F.: Rapid Antarctic ice sheet retreat under low atmospheric CO2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12028, https://doi.org/10.5194/egusphere-egu2020-12028, 2020.

EGU2020-13504 | Displays | CR1.2

Limited Retreat of the Wilkes Basin Ice Sheet during the Last Interglacial.

Johannes Sutter, Olaf Eisen, Martin Werner, Klaus Grosfeld, Thomas Kleiner, and Hubertus Fischer

The response of the marine sectors of the East Antarctic Ice Sheet to future global warming represents a major source of uncertainty in sea level projections. If greenhouse gas emissions continue unbridled, ice loss in these areas may contribute up to several meters to long-term global sea level rise. In East Antarctica, thinning of the ice cover of the George V and Sabrina Coast is currently taking place, and its destabilization in past warm climate periods has been implied. The extent of such past interglacial retreat episodes cannot yet be quantitatively derived from paleo proxy records alone. Ice sheet modelling constrained by paleo observations is therefore critical to assess the stability of the East Antarctic Ice Sheet during warmer climates. We propose that a runaway retreat during the Last Interglacial of the George V Coast grounding line into the Wilkes Subglacial Basin would either leave a clear imprint on the water isotope composition in the neighbouring Talos Dome ice-core record or prohibit the preservation of an ice core record from the Last Interglacial alltogether. We test this hypothesis using a dynamic ice sheet model and infer that the marine Wilkes Basin ice sheet remained stable throughout the Last Interglacial (130,000-120,000 years ago). Our analysis provides the first constraint on Last Interglacial East Antarctic grounding line stability by benchmarking ice sheet model simulations with ice core records. Our findings also imply that ambitious mitigation efforts keeping global temperature rise in check could safeguard this region from irreversible ice loss in the long term.

How to cite: Sutter, J., Eisen, O., Werner, M., Grosfeld, K., Kleiner, T., and Fischer, H.: Limited Retreat of the Wilkes Basin Ice Sheet during the Last Interglacial., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13504, https://doi.org/10.5194/egusphere-egu2020-13504, 2020.

EGU2020-13959 | Displays | CR1.2

Reconstructing the distribution of surface mass balance over East Antarctica (DML) from 1850 to present day

Nicolas Ghilain, Stéphane Vannitsem, Quentin Dalaiden, and Hugues Goosse

Over recent decades, the Antarctic Ice Sheet has witnessed large spatial variations at its surface through the surface mass balance (SMB). Since the complex Antarctic topography, working at high resolution is crucial to represent accurately the dynamics of SMB. While ice cores provide a mean to infer the SMB over centuries, the view is very spatially constrained. Global Climate models estimate the spatial distribution of SMB over centuries, but with a too coarse resolution with regards to the large variations due to local orographic effects. We have therefore explored a methodology to statistically downscale the SMB components from the climate model historical simulations (1850-present day). An analogue method is set up over a period of 30 years with the ERA-Interim reanalysis (1979-2010 AD) and associated with SMB components from the Regional Atmospheric Climate Model (RACMO) at 5 km spatial resolution over Dronning Maud in East Antarctica. The same method is then applied to the period from 1850 to present days using an ensemble of 10 simulations from the CESM2 model. This method enables to derive a spatial distribution of SMB. In addition, the changes in precipitation delivery mechanisms can be unveiled.

How to cite: Ghilain, N., Vannitsem, S., Dalaiden, Q., and Goosse, H.: Reconstructing the distribution of surface mass balance over East Antarctica (DML) from 1850 to present day, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13959, https://doi.org/10.5194/egusphere-egu2020-13959, 2020.

EGU2020-15081 | Displays | CR1.2

PISM paleo simulations of the Antarctic Ice Sheet over the last two glacial cycles

Torsten Albrecht, Ricarda Winkelmann, and Anders Levermann

Simulations of the glacial-interglacial history of the Antarctic Ice Sheet provide insights into dynamic threshold behavior and estimates of the ice sheet's contributions to global sea-level changes, for the past, present and future. However, boundary conditions are weakly constrained, in particular at the interface of the ice-sheet and the bedrock. We use the Parallel Ice Sheet Model (PISM) to investigate the dynamic effects of different choices of input data and of various parameterizations on the sea-level relevant ice volume. We evaluate the model's transient sensitivity to corresponding parameter choices and to different boundary conditions over the last two glacial cycles and provide estimates of involved uncertainties. We also present isolated and combined effects of climate and sea-level forcing on glacial time scales. 

How to cite: Albrecht, T., Winkelmann, R., and Levermann, A.: PISM paleo simulations of the Antarctic Ice Sheet over the last two glacial cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15081, https://doi.org/10.5194/egusphere-egu2020-15081, 2020.

EGU2020-16488 | Displays | CR1.2

Surface mass balance and melting projections over the Amundsen coastal region, West Antarctica

Nicolas Jourdain, Marion Donat-Magnin, Christoph Kittel, Cécile Agosta, Charles Amory, Hubert Gallée, Gerhard Krinner, and Mondher Chekki

We present Surface Mass Balance (SMB) and surface melt rates projections in West Antarctica for the end of the 21st century using the MAR regional atmosphere and firn model (Gallée 1994; Agosta et al. 2019) forced by a CMIP5-rcp85 multi-model-mean seasonal anomaly added to the ERA-Interim 6-hourly reanalysis.

 

First of all, we assess the validity of our projection method, following a perfect-model approach, with MAR constrained by the ACCESS-1.3 present-day and future climates. Changes in large-scale variables are well captured by our anomaly-based projection method, and errors on surface melting and SMB projections are typically 10%.

 

Based on the CMIP5-rcp85 multi-model mean, SMB over the grounded ice sheet in the Amundsen sector is projected to increase by 35% over the 21st century. This corresponds to a SMB sensitivity to near-surface warming of 8.3%.°C-1. Increased humidity, resulting from both higher water vapour saturation in warmer conditions and decreased sea-ice concentrations, are shown to favour increased SMB in the future scenario.

 

Ice-shelf surface melt rates at the end of the 21st century are projected to become 6 to 15 times larger than presently, depending on the ice shelf under consideration. This is due to enhanced downward longwave radiative fluxes related to increased humidity, and to an albedo feedback leading to more absorption of shortwave radiation. Interestingly, only three ice shelves produce runoff (Abbot, Cosgrove and Pine Island) in the future climate. For the other ice shelves (Thwaites, Crosson, Dotson, Getz), the future melt-to-snowfall ratio remains too low to produce firn air depletion and subsequent runoff.

 

How to cite: Jourdain, N., Donat-Magnin, M., Kittel, C., Agosta, C., Amory, C., Gallée, H., Krinner, G., and Chekki, M.: Surface mass balance and melting projections over the Amundsen coastal region, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16488, https://doi.org/10.5194/egusphere-egu2020-16488, 2020.

EGU2020-17355 | Displays | CR1.2

Decreasing Antarctic surface mass balance due to runoff-dominated ablation by 2100

Christoph Kittel, Charles Amory, Cécile Agosta, Nicolas Jourdain, Stefan Hofer, Alison Delhasse, and Xavier Fettweis

The surface mass balance (SMB) of the Antarctic ice sheet is often considered as a negative contributor to the sea level rise as present snowfall accumulation largely compensates for ablation through wind erosion, sublimation and runoff. The latter is even almost negligible since current Antarctic surface melting is limited to relatively scarce events over generally peripheral areas and refreezes almost entirely into the snowpack. However, melting can significantly affect the stability of ice shelves through hydrofracturing, potentially leading to their disintegration, acceleration of grounded ice and increased sea level rise. Although a large increase in snowfall is expected in a warmer climate, more numerous and stronger melting events could conversely lead to a larger risk of ice shelf collapse. In this study, we provide an estimation of the SMB of the Antarctic ice sheet for the end of the 21st century by forcing the state-of-the-art regional climate model MAR with three different global climate models. We chose the models (from both the Coupled Model Intercomparison Project Phase 5 and 6 - CMIP5 and CMIP6) providing the best metrics for representing the current Antarctic climate. While the increase in snowfall largely compensates snow ablation through runoff in CMIP5-forced projections, CMIP6-forced simulations reveal that runoff cannot be neglected in the future as it accounts for a maximum of 50% of snowfall and becomes the main ablation component over the ice sheet. Furthermore, we identify a tipping point (ie., a warming of 4°C) at which the Antarctic SMB starts to decrease as a result of enhanced runoff particularly over ice shelves. Our results highlight the importance of taking into account meltwater production and runoff and indicate that previous model studies neglecting these processes yield overestimated SMB estimates, ultimately leading to underestimated Antarctic contribution to sea level rise. Finally, melt rates over each ice shelf are higher than those that led to the collapse of the Larsen A and B ice shelves, suggesting a high probability of ice shelf collapses all over peripheral Antarctica by 2100.

How to cite: Kittel, C., Amory, C., Agosta, C., Jourdain, N., Hofer, S., Delhasse, A., and Fettweis, X.: Decreasing Antarctic surface mass balance due to runoff-dominated ablation by 2100, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17355, https://doi.org/10.5194/egusphere-egu2020-17355, 2020.

EGU2020-19278 | Displays | CR1.2

Feedback between ice dynamics and bedrock deformation with 3D viscosity in Antarctica

Wouter van der Wal, Caroline van Calcar, Bas de Boer, and Bas Blank

Over glacial-interglacial cycles, the evolution of an ice sheet is influenced by Glacial isostatic adjustment (GIA) via two negative feedback loops. Firstly, vertical bedrock deformation due to a changing ice load alters ice-sheet surface elevation. For example, an increasing ice load leads to a lower bedrock elevation that lowers ice-sheet surface elevation. This will increase surface melting of the ice sheet, following an increase of atmospheric temperature at lower elevations. Secondly, bedrock deformation will change the height of the grounding line of the ice sheet. For example, a lowering bedrock height following ice-sheet advance increases the melt due to ocean water that in turn leads to a retreat of the grounding line and a slow-down of ice-sheet advance.     
               GIA is mainly determined by the viscosity of the interior of the solid Earth which is radially and laterally varying. Underneath the Antarctic ice sheet, there are relatively low viscosities in West Antarctica and higher viscosities in East Antarctica, in turn affecting the response time of the above mentioned feedbacks. However, most ice-dynamical models do not consider the lateral variations of the viscosity in the GIA feedback loops when simulating the evolution of the Antarctic ice sheet. The method developed by Gomez et al. (2018) includes the feedback between GIA and ice-sheet evolution and alternates between simulations of the two models where each simulation covers the full time period. We presents a different method to couple ANICE, a 3-D ice-sheet model, to a 3-D GIA finite element model. In this method the model computations alternates between the ice-sheet and GIA model until convergence of the result occurs at each timestep. We simulate the evolution of the Antarctic ice sheet from 120 000 years ago to the present. The results of the coupled simulation will be discussed and compared to results of the uncoupled ice-sheet model (using an ELRA GIA model) and the method developed by Gomez et al. (2018).

How to cite: van der Wal, W., van Calcar, C., de Boer, B., and Blank, B.: Feedback between ice dynamics and bedrock deformation with 3D viscosity in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19278, https://doi.org/10.5194/egusphere-egu2020-19278, 2020.

EGU2020-19348 | Displays | CR1.2

Modelling the Antarctic Ice Sheet in the warm Mid-Pliocene

James O'Neill, Tamsin Edwards, Lauren Gregoire, Niall Gandy, Aisling Dolan, Andreas Wernecke, Stephen Cornford, Bas de Boer, Ilan Kelman, and Tina van de Flierdt

The Antarctic ice sheet is a deeply uncertain component of future sea level under anthropogenic climate change. To shed light on the ice sheets response to warmer climates in the past and its’ response to future warming, periods in Earth’s geological record can serve as instructive modelling targets. The mid-Pliocene warm period (3.3 – 3.0 Ma) is characterised by global mean surface temperatures ~2.7-4oC above pre-industrial, atmospheric CO2 concentrations of ~400ppm and eustatic sea level rise on the order of ~10-30m above modern. The mid-Pliocene sea level record is subject to large uncertainties. The upper end of this record implies a significant contribution from Antarctica and possible collapse of regions of the ice sheet, driven by marine ice sheet instabilities.

We present a suite of BISICLES ice sheet model simulations, forced with a subset of Pliocene Modelling Intercomparison Project (PlioMIP phase 1) coupled atmosphere-ocean climate models, that represent the Pliocene Antarctic ice sheet. This ensemble captures a range of possible ice sheet model responses to a warm Pliocene-like climate under different parameter choices, sampled in a Latin hypercube design. Modelled Antarctic sea level contribution is compared to reconstructions of Pliocene sea level, to explore the extent to which available data with large uncertainties can constrain the model parameter values.

Our aim with this work is to provide insights on Antarctic contribution to sea level in the warm mid-Pliocene. We seek to characterise the role of ice-ocean, ice-atmosphere and ice-bedrock parameter uncertainty in BISICLES on the ice sheet sea level contribution range, and whether cliff instability processes are necessary in reproduce high Pliocene sea levels in this ice sheet model.

How to cite: O'Neill, J., Edwards, T., Gregoire, L., Gandy, N., Dolan, A., Wernecke, A., Cornford, S., de Boer, B., Kelman, I., and van de Flierdt, T.: Modelling the Antarctic Ice Sheet in the warm Mid-Pliocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19348, https://doi.org/10.5194/egusphere-egu2020-19348, 2020.

EGU2020-20370 | Displays | CR1.2

Impact of coastal East Antarctic ice rises on surface mass balance: insights from observations and modelling

Thore Kausch, Stef Lhermitte, Jan T.M. Lenaerts, Nander Wever, Mana Inoue, Frank Pattyn, Sainan Sun, Sarah Wauthy, Jean-Louis Tison, and Willem Jan van de Berg

About 20% of all snow accumulation in Antarctica occurs on the ice shelfs and ice rises, locations within the ice shelf where the ice is locally grounded on topography. These ice rises largely control the spatial surface mass balance (SMB) distribution by inducing snowfall variability due to orographic uplift and by inducing wind erosion due altering the wind conditions. Moreover these ice rises buttress the ice flow and represent an ideal drilling locations for ice cores.

In this study we assess the connection between snowfall variability and wind erosion to provide a better understanding of how ice rises impact SMB variability, how well this is captured in the regional atmospheric climate model RACMO, and the implications of this SMB variability for ice rises as an ice core drilling side. By combining ground penetrating radar profiles from two ice rises in Dronning Maud Land with ice core dating we reconstruct spatial and temporal SMB variations across both ice rises from 1982 to 2017. Subsequently, the observed SMB is compared with output from RACMO, SnowModel to quantify the contribution of the different processes that control the spatial SMB variability across the ice rises. Finally, the observed SMB is compared with Sentinel-1 backscatter data to extrapolate spatial SMB trends over larger areas.

Our results show snowfall-driven differences of up to ~ 0.24 m w.e./yr between the windward and the leeward side of both ice rises as well as a local erosion driven minimum at the peak of the ice rises. RACMO captures the snowfall-driven differences, but overestimates their magnitude, whereas the erosion on the peak can be reproduced by SnowModel with RACMO forcing. Observed temporal variability of the average SMBs calculated for 4 time intervals in the 1982-2017 range are low at the peak of the easternmost ice rise (~ 0.03 m w.e./yr), while being three times higher (~ 0.1 m w.e./yr) on the windward side of the ice rise. This implicates that at the peak of the ice rise, higher snowfall, driven by regional processes, such as orographic uplift, is balanced out by local erosion.  Comparison of the observed SMB gradients with Sentinel-1 data finally shows the potential of SAR satellite observations to represent spatial variability in SMB across ice shelves and ice rises.

How to cite: Kausch, T., Lhermitte, S., Lenaerts, J. T. M., Wever, N., Inoue, M., Pattyn, F., Sun, S., Wauthy, S., Tison, J.-L., and van de Berg, W. J.: Impact of coastal East Antarctic ice rises on surface mass balance: insights from observations and modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20370, https://doi.org/10.5194/egusphere-egu2020-20370, 2020.

CR1.3 – Ice-Ocean-Atmosphere Interactions in West Antarctica and the Weddell Sea Sector

EGU2020-603 | Displays | CR1.3

Recent Changes in the Larsen-Weddell System

Ted Scambos

A warming planet, and particularly the warming Pacific Ocean, has led to major changes in the Larsen-Weddell System. While somewhat less significant than those in the adjacent Amundsen-Bellingshausen Sea and its coastal ice, the changes are nonetheless dramatic indicators of a closely interconnected system, driven by increased westerly winds and their impact on surface melting and ice drift. The system very likely will see further major changes if warming continues through the 22nd Century.

A warming trend in the central Pacific over the past ~80 years has induced air circulation changes over the Southern Ocean and Antarctic Peninsula. A rise in the mean speed of westerly-northwesterly winds across the northern Peninsula led to more frequent foehn events, which in turn increased surface melting on the eastern Peninsula ice shelves, and were responsible for reduced sea ice cover and more frequent shore leads on the eastern edges of the ice shelves. This likely led to greater sub-ice-shelf circulation, possibly including solar-warmed surface water (in summer) and modified Weddell Deep Water (mWDW). Around 1986, structural evidence in the form of more disrupted shear zones and increased rifting suggests that the Larsen A and B ice shelves began to thin and weaken. At this progressed, a combination of increased surface ponding and reduced backstress on the iceshelves led to a series of catastrophic break-ups due to hydrofracture, in 1995 (Larsen A shelf) and 2002 (Larsen B).  More recently, thinning detected by altimetry on the northern Larsen C may have contributed to new fracturing and calving of a large iceberg there in 2016 (iceberg A-68), setting the ice shelf front significantly farther to the west than has previously been observed (since 1898).

Looking forward, if the trend in increased westerly winds and Southern Annular Mode index continues, it is anticipated (modelled) that the large clockwise Weddell Gyre will increase in mean flow speed, and that warm deep water entrained from the Antarctic Circumpolar Current will more frequently mix with the mid- to deep ocean layers in the Weddell Gyre. One outcome of this is likely to be advection of warm deep water into the Ronne Ice Shelf cavity, dramatically increasing the heat available for sub-ice-shelf melting there and potentially changing ice sheet flux from the outlet glaciers significantly.

How to cite: Scambos, T.: Recent Changes in the Larsen-Weddell System , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-603, https://doi.org/10.5194/egusphere-egu2020-603, 2020.

The Weddell Polynya, a large hole in the winter sea ice cover, has intrigued researchers since satellite observations began in the late 70s. There is no consensus regarding the mechanisms leading to its opening, not least because there never was an instrument deployed early enough at the right location and with the right sampling interval. But what if we could predict imminent openings, by detecting early-warning signs from space?

The leading theory among oceanographers is that the polynya opens after the sea ice is melted from below by upwelled warm waters. We argue that such upwelling, or at least the increased heat flux through a thinning ice, should be visible on spaceborne thermal infrared imagery. Using microwave-based sea ice products to determine past polynya openings, we first found that there were in fact 83 Weddell / Maud Rise Polynya occurrences since winter 2000, 19 of which reaching an area larger than 1000 km2. We then created a timeseries of (cloud-filtered) daily mean brightness temperature at 3.7, 10.5 and 12 μm from Advanced Very High Resolution Radiometer datasets and found a significant warm temperature anomaly at least 10 days before the polynya opened, peaking at 4K for all bands 5-6 days before the opening. The anomaly is on average 2K stronger for the large polynyas (> 1000 km2). Moreover, the band ratios brutally change magnitude, which suggests lead formation rather than progressive melting – a hypothesis that would agree with meteorologists' theory that the polynya opens because of winds, and that we are now checking with spaceborne radar.

Six days is not much, but it would be enough to re-route expeditions or autonomous sensors so that the opening can be monitored in details. And this is only the first step of our ongoing project... stay tuned to see if we can predict weeks or months ahead!

How to cite: Heuzé, C. and Lemos, A.: Imminent re-opening of the Weddell Polynya detectable days ahead by spaceborne infrared , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3636, https://doi.org/10.5194/egusphere-egu2020-3636, 2020.

EGU2020-19812 | Displays | CR1.3

Polynya area and frequency in the Weddell Sea in CMIP6 climate models

Martin Mohrmann, Céline Heuzé, and Sebastiaan Swart

The presence of polynyas has a large effect on air-sea fluxes and deep water production, therefore impacting climate-relevant properties such as heat and carbon exchange between the atmosphere and ocean interior. One of the key areas of deep water formation is in the Weddell Sea, where much attention has recently been placed in the reoccurance of the open ocean Maud Rise polynya. In this study, two methods are presented to track the number, area and spatial distribution of polynyas with a focus on the Weddell Sea. The analysis is applied to a set of 10 Coupled Model Intercomparison Project phase 6 (CMIP6) models and to satellite sea ice concentration data. The first approach is a sea ice threshold method applied to the CMIP6 sea ice data at the original model grid. Open water areas surrounded by sea ice are classified as polynyas. Without requiring any remapping or interpolation, this method preserves the area information of all grid cells and is well suited to compute the combined area of the polynyas in the Weddell Sea. The second approach makes use of an image analysis technique to outline areas with low sea ice concentration. This method is preferable for counting the absolute number of polynyas and obtaining statistical information about their position. Satellite sea ice concentration is used as a reference to compare the performance of the models representing polynya area and to indicate model biases in the location of polynyas. All analyzed CMIP6 models show coastal polynyas, while only about half of the models regularly form open water polynyas. The resolution (about one degree for most models) sets a limit for the number of the polynyas in the numerical models.

How to cite: Mohrmann, M., Heuzé, C., and Swart, S.: Polynya area and frequency in the Weddell Sea in CMIP6 climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19812, https://doi.org/10.5194/egusphere-egu2020-19812, 2020.

EGU2020-10194 | Displays | CR1.3

A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea

Markus Janout, Hartmut Hellmer, Tore Hattermann, Svein Osterhus, Lucrecia Stulic, Oliver Huhn, Jürgen Sültenfuss, and Torsten Kanzow

The Filchner and Ronne ice sheets (FRIS) compose the second largest contiguous ice sheet on the Antarctic continent. Unlike at several other Antarctic glaciers, basal melt rates at FRIS are comparatively low, as cold and dense waters presently dominate the wide southern Weddell Sea (WS) continental shelf and effectively block out any significant inflow of warmer ocean waters. We revisited the southern WS shelf in austral summer 2018 during Polarstern expedition PS111 with detailed hydrographic and tracer measurements along both the Ronne and Filchner ice fronts. The hydrography along FRIS was characterized by near-freezing high salinity shelf water (HSSW) in front of Ronne, and a striking dominance of ice shelf water (ISW) in Filchner Trough. The cold (-2.2°C) and fresher (34.6) ISW was formed by the interaction of Ronne-sourced HSSW with the ice shelf base. The strong dominance of ISW in Filchner Trough indicates a recently enhanced circulation below FRIS, likely fueled by enhanced sea ice production in the southwestern WS. We view these recent observations in a multidecadal (1973-present) context, contrast the two dominant circulation modes below FRIS, and discuss the importance of sea ice formation and large-scale sea level pressure patterns for the stability of the ocean circulation and basal melt rates underneath FRIS.

How to cite: Janout, M., Hellmer, H., Hattermann, T., Osterhus, S., Stulic, L., Huhn, O., Sültenfuss, J., and Kanzow, T.: A recent update on the circulation and water masses around the Filchner and Ronne ice shelves in the southern Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10194, https://doi.org/10.5194/egusphere-egu2020-10194, 2020.

EGU2020-19934 | Displays | CR1.3

Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica

Anna Wåhlin, Bastien Queste, Alastair Graham, Kelly Hogan, Lars Boehme, Karen Heywood, Robert Larter, Erin Pettit, and Julia Wellner

The fate of the West Antarctic Ice Sheet is the largest remaining uncertainty in predicting sea-level rise through the next century, and its most vulnerable and rapidly changing outlet is Thwaites Glacier . Because the seabed slope under the glacier is retrograde (downhill inland), ice discharge from Thwaites Glacier is potentially unstable to melting of the underside of its floating ice shelf and grounding line retreat, both of which are enhanced by warm ocean water circulating underneath the ice shelf. Recent observations show surprising spatial variations in melt rates, indicating significant knowledge gaps in our understanding of the processes at the base of the ice shelf. Here we present the first direct observations of ocean temperature, salinity, and oxygen underneath Thwaites ice shelf collected by an autonomous underwater vehicle, a Kongsberg Hugin AUV. These observations show that while the western part of Thwaites has outflow of meltwater-enriched circumpolar deep water found in the main trough leading to Thwaites, the deep water (> 1000 m) underneath the central part of the ice shelf is in connection with Pine Island Bay - a previously unknown westward branch of warm deep water flow. Mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point and large spatial gradients of salinity and temperature indicate that this is a region of active mixing processes. The observations challenge conceptual models of ice-ocean interactions at glacier grounding zones and identify a main buttressing point as a vulnerable region of change currently under attack by warm water inflow from all sides: a scenario that may lead to ungrounding and retreat more quickly than previously expected.

How to cite: Wåhlin, A., Queste, B., Graham, A., Hogan, K., Boehme, L., Heywood, K., Larter, R., Pettit, E., and Wellner, J.: Warm water flow and mixing beneath Thwaites Glacier ice shelf, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19934, https://doi.org/10.5194/egusphere-egu2020-19934, 2020.

EGU2020-245 | Displays | CR1.3

Pathways of ocean heat towards Pine Island and Thwaites grounding lines

Yoshihiro Nakayama, Georgy Manucharyan, Hong Zhang, Pierre Dutrieux, Hector S. Torres, Patrice Klein, Helene Seroussi, Michael Schodlok, Eric Rignot, and Dimitris Menemenlis

In the Amundsen Sea, modified Circumpolar Deep Water (mCDW) intrudes into ice shelf cavities, causing high ice shelf melting near the ice sheet grounding lines, accelerating ice flow, and controlling the pace of future Antarctic contributions to global sea level. The pathways of mCDW towards grounding lines are crucial as they directly control the heat reaching the ice. A realistic representation of mCDW circulation, however, remains challenging due to the sparsity of in-situ observations and the difficulty of ocean models to reproduce the available observations. In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments inqualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104ºW and 74.3ºS. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates. 


We also briefly introduce our various existing model outputs focusing on the Amundsen Sea and demonstrate how to access these model outputs, plot some basic variables, and create animations. We hope that these model output can be utilized for many different aspects of oceanographic researches including observational planning, data analysis for physical, biological and chemical oceanography, and boundary conditions for ocean and ice sheet models. 

 

How to cite: Nakayama, Y., Manucharyan, G., Zhang, H., Dutrieux, P., S. Torres, H., Klein, P., Seroussi, H., Schodlok, M., Rignot, E., and Menemenlis, D.: Pathways of ocean heat towards Pine Island and Thwaites grounding lines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-245, https://doi.org/10.5194/egusphere-egu2020-245, 2020.

EGU2020-8411 | Displays | CR1.3 | Highlight

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers

David Lilien, Ian Joughin, Benjamin Smith, and Noel Gourmelen

Smith, Pope, and Kohler glaciers and the corresponding Crosson and Dotson ice shelves have undergone speedup, thinning, and rapid grounding-line retreat in recent years, leaving them in a state likely conducive to future retreat. We conducted a suite of numerical model simulations of these glaciers and compared the results to observations to determine the processes controlling their recent evolution. Simulations were forced using estimates of the distribution and intensity of melt from 1996-2014. The model simulations indicate that the state of these glaciers in the 1990s was not inherently unstable, i.e., that small perturbations to the grounding line would not necessarily have caused the large retreat that has been observed. Instead, sustained melt, at rates higher than the 1990s and concentrated at the grounding line, was needed to cause the observed retreat. Weakening of the margins of Crosson Ice Shelf may have hastened the onset of grounding-line retreat but is unlikely to have initiated these rapid changes without an accompanying increase in melt. In the simulations that most closely match the observed thinning, speedup, and retreat, modeled grounding-line retreat and ice loss continue unabated throughout the 21st century, and subsequent retreat along Smith Glacier's trough appears likely. Given the modeled retreat, thinning associated with the retreat of Smith Glacier may reach the ice divide and undermine a portion of the Thwaites catchment as quickly as changes initiated at the Thwaites terminus. Thus, while the Smith, Pope, Kohler catchment is small compared to Thwaites, these smaller glaciers may be important when considering the centennial-scale evolution of the Amundsen Sea region.

How to cite: Lilien, D., Joughin, I., Smith, B., and Gourmelen, N.: Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler Glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8411, https://doi.org/10.5194/egusphere-egu2020-8411, 2020.

EGU2020-20152 | Displays | CR1.3

The importance of sea ice biota for the ecosystem in the northwestern Weddell Sea

Ilka Peeken, Stefanie Arndt, Markus Janout, Thomas Krumpen, and Christian Haas

The western Weddell Sea along the northward branch of the Weddell Gyre is a region of major outflow of various water masses, thick sea ice, and biogeochemical matter, linking the Antarctic continent to the world oceans. It features a deep shelf and the second largest ice shelf (Larsen C) in the WS, and its perennial sea ice cover is among the thickest on earth. This region is undergoing dramatic changes due to the breakup of ice shelves along the Antarctic Peninsula, which results in oceanographic conditions unprecedented in the past 10,000 years. Since this region is difficult to access, comprehensive physical and biogeochemical information is still lacking. During the interdisciplinary Weddell Sea Ice (WedIce) expedition to the northwestern Weddell Sea on board the German icebreaker RV Polarstern in spring 2019, oceanographic and biogeochemical studies were conducted together with in-situ snow and ice sampling. Most stations visited contained second- and third-year ice. Additional airborne ice-thickness surveys revealed a mean ice thicknesses between 2.6 and 5.4 m, increasing from the Antarctic Sound towards the Larsen B region. Usually rotten ice was present below a solid, ~30 cm thick surface-ice layer, however, pronounced gap layers, typical for late summer ice in the marginal ice zone, were rare. The associated high algal biomass was only found north of the Antarctic Sound. Nevertheless, diatom-dominated standing stocks of integrated sea ice algae biomass were among the highest, previously described in Antarctic waters. In contrast, despite overall high macro-nutrient concentrations in the water, the biomass of the flagellate dominated phytoplankton was negligible for primary production in the entire region. Overall, it seems that despite changing light conditions for the phytoplankton due to the loss of ice shelves, the sea ice-derived carbon represents an important control variable for higher trophic levels in the western Weddell Sea.

How to cite: Peeken, I., Arndt, S., Janout, M., Krumpen, T., and Haas, C.: The importance of sea ice biota for the ecosystem in the northwestern Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20152, https://doi.org/10.5194/egusphere-egu2020-20152, 2020.

EGU2020-253 | Displays | CR1.3

New observations of late summer bio-physical ice and snow conditions in the northwestern Weddell Sea

Stefanie Arndt, Christian Haas, and Ilka Peeken

Summer sea ice extent in the Weddell Sea has increased overall during the last four decades, with large interannual variations. However, the underlying causes and the related ice and snow properties are still poorly known. Here we present results of the interdisciplinary Weddell Sea Ice (WedIce) project carried out in the northwestern Weddell Sea on board the German icebreaker R/V Polarstern in February and March 2019, i.e. at the end of the summer ablation period. This is the region of the thickest, oldest ice in the Weddell Sea, at the outflow of the Weddell Gyre. Measurements included airborne ice thickness surveys and in-situ snow and ice sampling of mostly second- and third year ice. Preliminary results show mean ice thicknesses between 2.6 and 5.4 m, increasing from the Antarctic Sound towards the Larsen B region. The ice had mostly positive ice freeboard. Mean snow thicknesses ranged between 0.05 and 0.46 m. Snow was well below the melting temperature on most days and was highly metamorphic and icy, with melt-freeze forms as dominant snow type. In addition, as a result of the summer’s thaw, an average of 0.14 m of superimposed ice was found in all ice cores drilled during the cruise. Although there was rotten ice below a solid, ca. 30 cm thick surface ice layer, pronounced gap layers typical for late summer ice in the marginal ice zone were rare, and algal biomass was patchily distributed within individual sea ice cores. Overall, there was a strong gradient of increasing ice algal biomass from the Larsen B to the Antarctic Sound region. The presented results show that sea ice conditions in the northwestern Weddell Sea are still severe and have not changed significantly since the last observations carried out in 2004 and 2006. The presence of relatively thin, icy snow has strong implications for the ice and snow mass balance, for freshwater oceanography, and for the application of remote sensing methods. Overall sea ice properties strongly affect the biological productivity of this region and limit carbon fluxes to the seafloor in the northwestern Weddell Sea.

How to cite: Arndt, S., Haas, C., and Peeken, I.: New observations of late summer bio-physical ice and snow conditions in the northwestern Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-253, https://doi.org/10.5194/egusphere-egu2020-253, 2020.

EGU2020-17323 | Displays | CR1.3

Lessons learnt from the former bed of Thwaites Glacier: a new multibeam-bathymetric dataset

Kelly Hogan, Robert Larter, Alastair Graham, Robert Arthern, James Kirkham, Rebecca Totten Minzoni, Tom Jordan, Rachel Clark, Victoria Fitzgerald, John Anderson, Claus-Dieter Hillenbrand, Frank Nitsche, Lauren Simkins, James Smith, Karsten Gohl, Jan Erik Arndt, Jongkuk Hong, and Julia Wellner

The coastal bathymetry of Thwaites Glacier (TG) is poorly known yet nearshore sea-floor highs have the potential to act as pinning points for floating ice shelves, or to block warm water incursions to the grounding line. In contrast, deeper areas control warm water routing. Here, we present more than 2000 km2 of new multibeam echo-sounder data (MBES) acquired offshore TG during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project on the RV/IB Nathaniel B. Palmer (NBP19-02) in February-March 2019. Beyond TG, the bathymetry is dominated by a >1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some sea-floor highs having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf. In addition, submarine landform evidence indicates at least some unconsolidated sediment cover on the highs, as well as in the troughs that separate them. Knowing that this offshore area of ridges and troughs is a former bed for TG, we also used a novel spectral approach and existing ice-flow theory to investigate bed roughness and basal drag over the newly-revealed offshore topography. We show that the sea-floor bathymetry is a good analogue for extant bed areas of TG and that ice-sheet retreat over the sea-floor troughs and ridges would have been affected by high basal drag similar to that acting in the grounding zone today.

Comparisons of the new MBES data with existing regional compilations show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the oceanic heat flux may be significantly underestimated. This work supports the findings of recent numerical ice-sheet and ocean modelling studies that recognise the need for accurate and high-resolution bathymetry to determine warm water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.

How to cite: Hogan, K., Larter, R., Graham, A., Arthern, R., Kirkham, J., Totten Minzoni, R., Jordan, T., Clark, R., Fitzgerald, V., Anderson, J., Hillenbrand, C.-D., Nitsche, F., Simkins, L., Smith, J., Gohl, K., Arndt, J. E., Hong, J., and Wellner, J.: Lessons learnt from the former bed of Thwaites Glacier: a new multibeam-bathymetric dataset, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17323, https://doi.org/10.5194/egusphere-egu2020-17323, 2020.

EGU2020-1567 | Displays | CR1.3

Complex, evolving patterns of mass loss from Antarctica’s largest glacier

Jonathan Bamber and Geoffrey Dawson

Pine Island Glacier (PIG) has contributed more to sea level rise over the last four decades than any other glacier in Antarctica. Model projections indicate that this will continue in the future but at conflicting rates, depending partly on the model initialisation. Some models suggest that mass loss could dramatically increase over the next few decades, resulting in a rapidly growing contribution to sea level, and fast retreat of the grounding line. Other models indicate more moderate losses. Resolving this contrasting behaviour is important for sea level rise projections as PIG and the Amndsen Sea Sector have been used as calibration for plausibility, probabilistic and deterministic approaches. Here, we use high resolution satellite observations of elevation change since 2010 from CryoSat-2 swath data to show that thinning rates are now highest along the slow-flow margins of the glacier and that the present-day amplitude and pattern of elevation change is inconsistent with fast grounding line migration and the associated rapid increase in mass loss over the next few decades. Instead, our results support model simulations that imply only modest changes in grounding line location over that timescale. We demonstrate how the pattern of thinning is evolving in complex ways both in space and time and how rates in the fast-flowing central trunk have decreased by about a factor five since 2007. We also consider how the complex pattern of mass loss affects the interpretation of vertical land motion from GPS data and inferences made from these data for mantle viscosity and solid Earth response times.

 

How to cite: Bamber, J. and Dawson, G.: Complex, evolving patterns of mass loss from Antarctica’s largest glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1567, https://doi.org/10.5194/egusphere-egu2020-1567, 2020.

EGU2020-1304 | Displays | CR1.3

Reflection Seismic Interpretation of Topography and Acoustic Impedance beneath Thwaites Glacier, West Antarctica

Elisabeth Clyne, Sridhar Anandakrishnan, Atsuhiro Muto, Richard Alley, Donald Voight, and Kiya Riverman

Thwaites Glacier (TG), West Antarctica, is losing mass in response to oceanic forcing. Future evolution could lead to deglaciation of the marine basins of the West Antarctic ice sheet, depending on ongoing and future climate forcings, but also on basal topography/bathymetry, basal properties, and physical processes operating within the grounding zone. Hence, it is important to know the actual distribution of bed types of TG’s interior and grounding zone, and to incorporate them accurately in models to improve estimates of retreat rates and stability. Here we determine bed reflectivity and acoustic impedance via amplitude analysis of reflection seismic data. We report on the results from two lines – a longitudinal (L-Line) and a transverse (N-Line) – on a central flowline of TG 100 km inland from the grounding zone. There is considerable variability in bed forms and properties, both within this dataset and in-comparison with nearby work. Notably, we find the same hard (bedrock) stoss and soft (till) lee pattern observed elsewhere on TG in prior work. Physical understanding indicates the basal flow law describing motion over different regions of TG’s bed likely varies from nearly viscous over the hard bedrock regions to nearly plastic over soft till regions, providing a template for modeling.

How to cite: Clyne, E., Anandakrishnan, S., Muto, A., Alley, R., Voight, D., and Riverman, K.: Reflection Seismic Interpretation of Topography and Acoustic Impedance beneath Thwaites Glacier, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1304, https://doi.org/10.5194/egusphere-egu2020-1304, 2020.

EGU2020-1603 | Displays | CR1.3 | Highlight

Submarine landforms on the Weddell Sea shelf imaged at high resolution using AUVs

Julian Dowdeswell, Christine Batchelor, Sasha Montelli, Dag Ottesen, Evelyn Dowdeswell, and Jeffrey Evans

Multibeam echo-sounders were deployed from Autonomous Underwater Vehicles (AUVs) flying close to the seafloor of the Weddell Sea shelf in order to investiagte the glacial landforms there with a view to understanding processes and patterns associated with deglaciation from the Last Glacial Maximum on the eastern side of the Antarctic Peninsula. A horizontal resolution of 0.5 m (using conventional mulitbeam systems), and in some cases 0.05 m (using interferometric multibeam equipment), allowed delicate seafloor landforms to be mapped in several areas of the shelf beyond the Larsen C and former Larsen A and B ice shelves. A number of glacial landform assemblages were observed, including suites of delicate ridges associated with grounding-zone wedges and the grounding of icebergs on the shelf. These landforms are probably related to the action of tides moving the ice up and down through a series of tidal cycles. At the highest spatial resolution, individual dropstones derived from rain-out during the melting of floating ice were imaged clearly. Imaging the seafloor at such high resolution allows both very detailed descriptions of submarine landform morphology and also the complexity of such landforms and landform assemblages to be better understood, aiding the interpretation of the glacial and related processes that led to their formation.

How to cite: Dowdeswell, J., Batchelor, C., Montelli, S., Ottesen, D., Dowdeswell, E., and Evans, J.: Submarine landforms on the Weddell Sea shelf imaged at high resolution using AUVs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1603, https://doi.org/10.5194/egusphere-egu2020-1603, 2020.

EGU2020-20512 | Displays | CR1.3 | Highlight

The Grounding Zone of Thwaites Glacier Explored by Icefin

Britney Schmidt, Keith Nicholls, Peter Davis, James Smith, Kiya Riverman, David Holland, Daniel Dichek, Andrew Mullen, Justin Lawrence, Peter Washam, Aurora Basinski-ferris, Paul Anker, Matthew Meister, Anthony Spears, Ben Hurwitz, Enrica Quartini, Elisabeth Clyne, Catrin Thomas, James Wake, and David Vaughn and the ITGC Team (MELT & Thwaites Glacier Grounding Zone Downstream teams)

Icefin performed the first long range robotic exploration of the grounding zone of Thwaites Glacier from January 9-12 2020. Icefin was part of the MELT project of the International Thwaites Glacier Collaboration deployed to the grounding zone of Thwaites Glacier, West Antarctica over the period December 2019-February 2020.  MELT is an interdisciplinary project to explore rapid change across the grounding zone, and in particular basal melting.  The subglacial cavity ~2km north of the grounding zone was accessed via hot water drilling on January 7-8, 2020.  Icefin, a hybrid autonomous and remotely operated underwater vehicle designed for sub-ice and borehole operations, conducted over 15km of round-trip data collection under the ice along a section of the glacier from the grounding zone extending to a point 4 km oceanward.   The vehicle collected data with ten different science sensors including cameras, sonars, conductivity/temperature and dissolved oxygen.  Overall, the water column ranged from ~100m downstream that narrowed quickly to an average of 50m that spanned over 2km, to a long segment of ~30m thickness before quickly narrowing over 500m towards the grounding zone. The seafloor structures run roughly parallel to ice flow direction, consisting of furrows, ridges, and grooves in some cases mirrored by the ice structure. The Icefin dives revealed a diverse set of basal ice conditions, with complex geometry, including a range of terraced features, smooth ablated surfaces, crevassing, sediment rich layers of varying kinds, as well as interspersed clear, potentially accreted freshwater ice.  The ocean directly beneath the ice varies spatially, from moderately well-mixed near the grounding zone to highly stratified within and below concavities in the ice downstream.  Sediments along the sea floor range from fine grained downstream to course angular gravel near the grounding zone distributed between larger boulders.  We observed rocky material in the ice that ranged from fine grained layers compressed within the ice to small angular particles volumetrically distributed within ice, to gravel and cobbles, as well as trapped boulders up to meter scale. In addition to the oceanographic, glaciological and sea floor conditions, we also catalogued communities of organisms along the seafloor and ice-ocean interface. We will report the highlights and initial conclusions from Icefin’s in situ data collection, and offer perspectives on change at the grounding zone.

How to cite: Schmidt, B., Nicholls, K., Davis, P., Smith, J., Riverman, K., Holland, D., Dichek, D., Mullen, A., Lawrence, J., Washam, P., Basinski-ferris, A., Anker, P., Meister, M., Spears, A., Hurwitz, B., Quartini, E., Clyne, E., Thomas, C., Wake, J., and Vaughn, D. and the ITGC Team (MELT & Thwaites Glacier Grounding Zone Downstream teams): The Grounding Zone of Thwaites Glacier Explored by Icefin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20512, https://doi.org/10.5194/egusphere-egu2020-20512, 2020.

The distribution and concentration of sea ice presents a significant challenge to shipping and scientific expeditions in high-latitude regions. In addition to achieving safe navigation, information about likely sea ice conditions is needed for expedition planning, and the deployment and retrieval of scientific instruments and their data. In areas where time series of passive microwave data exist, broad-scale analysis of sea ice concentration can be readily achieved. However, the spatial resolution of these data does not permit detailed investigations of sea ice conditions, including near-shore lead development.

Here we present a new methodology for processing moderate resolution multispectral and thermal satellite imagery to summarise inter-annual differences in the probability of sea ice observation. By using multiple daily imagery sources (Terra and Aqua MODIS; Suomi-NPP VIIRS), and averaging resultant concentration maps over longer time periods, we reduce the impediment of cloud cover to characterising sea ice using this type of imagery. Our processing provides a higher-resolution depiction of sea ice conditions and their variability than that afforded by passive microwave data. By estimating a sub-pixel concentration for all pixels identified as ‘Ice’, we capture further nuances of narrower water/thin ice inclusions within the ice cover.

The utility of this new methodology to support operational ship survey in polar regions is demonstrated using examples from the Weddell Sea, Antarctica. Our description of sea ice cover agrees well with that derived from very high-resolution imagery from the Operation Ice Bridge DMS camera system, and with experience of the actual sea ice conditions encountered during the Weddell Sea Expedition in early 2019.

How to cite: Benham, T., Christie, F., and Dowdeswell, J.: Sea ice in the Weddell Sea: use of moderate resolution imagery to summarize inter-annual variation in conditions and support operational ship survey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21821, https://doi.org/10.5194/egusphere-egu2020-21821, 2020.

EGU2020-21896 | Displays | CR1.3

The Weddell Sea Expedition 2019

John Shears, Julian Dowdeswell, Freddie Ligthelm, and Paul Wachter

The Weddell Sea Expedition 2019 (WSE) was conceived with dual aims: (i) to undertake a comprehensive international inter-disciplinary programme of science centred in the waters around Larsen C Ice Shelf, western Weddell Sea; and (ii) to search for, survey and image the wreck of Sir Ernest Shackleton’s Endurance, which sank in the Weddell Sea in 1915. 

The 6-week long expedition, funded by the Flotilla Foundation, required the use of a substantial ice-strengthened vessel given the very difficult sea-ice conditions encountered in the Weddell Sea, and especially in its central and western parts. The South African ship SA Agulhas II was chartered for its Polar Class 5 icebreaking capability and design as a scientific research vessel. The expedition was equipped with state-of-the-art Autonomous Underwater Vehicles (AUVs) and a Remotely Operated Vehicle (ROV) which were capable of deployment to waters more than 3,000 m deep, thus making the Larsen C continental shelf and slope, and the Endurance wreck site, accessible. During the expedition, a suite of passive and active remote-sensing data, including TerraSAR-X radar images delivered in near real-time, was provided to the ice-pilot onboard the SA Agulhas II. These data were instrumental for safe vessel navigation in sea ice and the detection and tracking of icebergs and ice floes of scientific interest.

The scientific programme undertaken by the WSE was very successful and produced many new geological, geophysical, marine biological and oceanographic observations from a part of the Weddell Sea that has been little studied previously, particularly the area east of Larsen C Ice Shelf. The expedition also reached the sinking location of Shackleton’s Endurance, where the presence of open-water sea ice leads allowed the deployment of an AUV to the ocean floor to try and locate and survey the wreck. Unfortunately, SA Agulhas II later lost communication with the AUV, and deteriorating weather and sea ice conditions meant that the search had to be called off.

How to cite: Shears, J., Dowdeswell, J., Ligthelm, F., and Wachter, P.: The Weddell Sea Expedition 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21896, https://doi.org/10.5194/egusphere-egu2020-21896, 2020.

EGU2020-7801 | Displays | CR1.3

Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation

Frazer Christie, Toby Benham, and Julian Dowdeswell

The Antarctic Peninsula is one of the most rapidly warming regions on Earth. There, the recent destabilization of the Larsen A and B ice shelves has been directly attributed to this warming, in concert with anomalous changes in ocean circulation. Having rapidly accelerated and retreated following the demise of Larsen A and B, the inland glaciers once feeding these ice shelves now form a significant proportion of Antarctica’s total contribution to global sea-level rise, and have become an exemplar for the fate of the wider Antarctic Ice Sheet under a changing climate. Together with other indicators of glaciological instability observable from satellites, abrupt pre-collapse changes in ice shelf terminus position are believed to have presaged the imminent disintegration of Larsen A and B, which necessitates the need for routine, close observation of this sector in order to accurately forecast the future stability of the Antarctic Peninsula Ice Sheet. To date, however, detailed records of ice terminus position along this region of Antarctica only span the observational period c.1950 to 2008, despite several significant changes to the coastline over the last decade, including the calving of giant iceberg A-68a from Larsen C Ice Shelf in 2017.

Here, we present high-resolution, annual records of ice terminus change along the entire western Weddell Sea Sector, extending southwards from the former Larsen A Ice Shelf on the eastern Antarctic Peninsula to the periphery of Filchner Ice Shelf. Terminus positions were recovered primarily from Sentinel-1a/b, TerraSAR-X and ALOS-PALSAR SAR imagery acquired over the period 2009-2019, and were supplemented with Sentinel-2a/b, Landsat 7 ETM+ and Landsat 8 OLI optical imagery across regions of complex terrain.

Confounding Antarctic Ice Sheet-wide trends of increased glacial recession and mass loss over the long-term satellite era, we detect glaciological advance along 83% of the ice shelves fringing the eastern Antarctic Peninsula between 2009 and 2019. With the exception of SCAR Inlet, where the advance of its terminus position is attributable to long-lasting ice dynamical processes following the disintegration of Larsen B, this phenomenon lies in close agreement with recent observations of unchanged or arrested rates of ice flow and thinning along the coastline. Global climate reanalysis and satellite passive-microwave records reveal that this spatially homogenous advance can be attributed to an enhanced buttressing effect imparted on the eastern Antarctic Peninsula’s ice shelves, governed primarily by regional-scale increases in the delivery and concentration of sea ice proximal to the coastline.

How to cite: Christie, F., Benham, T., and Dowdeswell, J.: Recent glacial advance in the western Weddell Sea Sector driven by anomalous sea ice circulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7801, https://doi.org/10.5194/egusphere-egu2020-7801, 2020.

EGU2020-20610 | Displays | CR1.3

Sea ice characteristics during the Weddell Sea expedition explored by geophysical and remote sensing methods

Wolfgang Rack, Frazer Christie, Evelyn Dowdeswell, Julian Dowdeswell, Paul Wachter, Toby Benham, Christian Haas, and Paul Bealing

The 2019 Weddell Sea expedition provided a unique opportunity for geophysical and glaciological sea ice measurements in one of the least accessible regions of the Southern Ocean. Although the extent and area of sea ice is well known based on satellite measurements, the limited information on thickness does still hinder the calculation of trends trends in volume and mass. Sea ice thickness is therefore one of the missing key variables in the global cryosphere mass balance, and difficult logistics are a challenge for near synchronous satellite validation measurements. Another key variable in this context is snow on sea ice, as knowledge of snow is required to convert satellite-derived freeboard to thickness.

We measured the sea-ice morphology by a combination of on ice and remote sensing methods: near-synchronous temporal and spatial measurements from a drone equipped with a radar sensor and camera, manually-derived on-ice surveys and samples such as snow pits, snow-depth transects and drill holes, and a AUV with upward-looking multibeam sonars. We also deployed ice-drifter buoys on several ice floes which we used to provide floe drift over an extended period of time.

In this contribution we present the results of our observations in conjunction with a close sequence of high resolution satellite radar images (TerraSAR-X, Sentinel-1) and altimeter data (ICESat-2 and CryoSat-2) to characterise the sea ice conditions in the western Weddell Sea. We found a mixture of fragments of deformed first-year and multi-year sea-ice which was consolidated in larger ice floes. A thick snow cover frequently depressed the ice cover of the thinner first year ice below sea level. Satellite data allow to extend our findings in time to a larger area and to improve our information on sea ice over a larger region.

How to cite: Rack, W., Christie, F., Dowdeswell, E., Dowdeswell, J., Wachter, P., Benham, T., Haas, C., and Bealing, P.: Sea ice characteristics during the Weddell Sea expedition explored by geophysical and remote sensing methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20610, https://doi.org/10.5194/egusphere-egu2020-20610, 2020.

EGU2020-1330 | Displays | CR1.3

Post-disintegration evolution of the largest Larsen B tributary glaciers

Ted Scambos, Jennifer Bohlander, and Karen Alley

Crane and Hektoria glaciers, the major tributaries of the former Larsen B Ice Shelf, underwent major structural and ice flow changes in the aftermath of the ice shelf’s disintegration in March, 2002. In addition to the widely reported initial acceleration (leading to speeds 3 to 6 times the pre-disintegration rate), the continued retreat led to the formation of significant ice cliffs. For Hektoria, this occurred as a seamless transition from ice shelf disintegration. Crane Glacier had a two-stage acceleration, first increasing in speed by 3x in the first few months after disintegration, then slowing through September 2004, and then a rapid additional acceleration in 2005-2006. Both glaciers developed significant ice cliffs during retreat, with peak ice-front heights of 105 m for Crane and 85 m for Hektoria.

How to cite: Scambos, T., Bohlander, J., and Alley, K.: Post-disintegration evolution of the largest Larsen B tributary glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1330, https://doi.org/10.5194/egusphere-egu2020-1330, 2020.

EGU2020-18507 | Displays | CR1.3

Meltwater and circulation characteristics adjacent to Larsen C ice shelf: insights from seawater oxygen isotopes

Joshua Mirkin, Adam West, Katherine Hutchinson, Raquel Flynn, and Sarah Fawcett

The Larsen C ice shelf (LCIS) in the western Weddell Sea has recently undergone large-scale ice shelf collapse with the detachment of iceberg A68 in 2017. Cold cavity ice shelves, such as LCIS, are critical for the formation of the world’s coldest, densest waters and act to prevent the flow of land-fast ice into the ocean, which would result in sea-level rise. Their disintegration is thus of great scientific interest and growing public concern. It has been hypothesized that ice shelf breakup may result from ice shelf thinning, which can be caused by densification through surface processes, a decrease in grounded ice flow, or increased surface or basal melting. To investigate whether ice shelf melting may be contributing to the collapse of LCIS, we collected full depth profiles of seawater samples at 17 stations in the vicinity of LCIS in January 2019 during the Weddell Sea Expedition. To investigate the formation processes and distribution of water masses, as well as identify regions of ice shelf melt, the samples were measured for seawater oxygen isotopic composition (δ18O) using a Picarro Cavity Ring-Down Spectroscope (CRDS). The isotope data provide little evidence of large-scale surface or basal ice shelf melting, with basal ice shelf melt constituting a maximum of 0.5% of the Ice Shelf Water (ISW) observed in the vicinity of LCIS. One implication of this is that surface and basal melting may not be the primary factor driving the collapse of LCIS, although more data and further study are required to confirm this. In addition, the isotope data are consistent with previous work suggesting that the onshore advection of warm offshore waters occurs via the Jason Trough, a remnant depression in the seafloor caused by the flow of a palaeo-ice stream. This, in combination with the observation (based on incorporating seawater δ18O into a temperature-salinity-oxygen mass balance model) that the outflow of ISW occurs primarily to the north of the study region, supports a clockwise circulation pattern in the vicinity of LCIS.

How to cite: Mirkin, J., West, A., Hutchinson, K., Flynn, R., and Fawcett, S.: Meltwater and circulation characteristics adjacent to Larsen C ice shelf: insights from seawater oxygen isotopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18507, https://doi.org/10.5194/egusphere-egu2020-18507, 2020.

EGU2020-2726 | Displays | CR1.3

Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea

Aleksandr Montelli, Christine Batchelor, Dag Ottesen, Julian Dowdeswell, Jeff Evans, and Evelyn Dowdeswell

Linear to curvilinear depressions interpreted as iceberg ploughmarks are identified on the continental shelf beyond Larsen C Ice Shelf in about 350 m water depth using multibeam echo-sounding at sub-metre horizontal resolution. Detailed imaging of ploughmark morphology demonstrates the presence of irregularly spaced ridges extending across the full ploughmark width. These ridges have an arcuate shape in plan-view, are up to 2 m high, 20-40 m wide, show occasional presence of subdued debris-flow lobes on their distal side and have an asymmetric cross-profile in which the seafloor deepens beyond their slightly steeper side. The ridges are interpreted to have been produced when the iceberg moved backwards under the falling tide, which pushed up a ridge of sediment behind the iceberg keel, before it continued on its original trajectory under the rising tide. Similar features, which we term ‘iceberg tidal ridges’, can be identified at lower resolution on bathymetric and three-dimensional seismic data from the mid-Norwegian margin, suggesting the broader implications of the interpretations presented here. For example, the mapping of delicate ridges preserved within iceberg ploughmarks can be used to reconstruct past oceanic circulation including the former direction and strength of ocean currents.

How to cite: Montelli, A., Batchelor, C., Ottesen, D., Dowdeswell, J., Evans, J., and Dowdeswell, E.: Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2726, https://doi.org/10.5194/egusphere-egu2020-2726, 2020.

EGU2020-16776 | Displays | CR1.3

The horizontal circulation, upwelling and heat budget of the Weddell Gyre: an observation perspective

Krissy Reeve, Torsten Kanzow, Mario Hoppema, Olaf Boebel, Volker Strass, Walter Geibert, and Rüdiger Gerdes

The Weddell Gyre is an important region in that it feeds source water masses (and thus heat) toward the ice-shelves, and exports locally and remotely formed dense water masses to the global abyssal ocean. Argo float profiles and trajectories were implemented to capture the large-scale, long-term mean circulation of the entire Weddell Gyre, from which the heat budget has been diagnosed for a layer within Warm Deep Water (WDW), the main heat source to the Weddell Gyre. We show that heat is horizontally advected into the southern limb of the Weddell Gyre, and then removed from the southern limb by horizontal turbulent diffusion (1) northwards towards the gyre interior, and (2) southwards towards the ice shelves. Since the gyre is cyclonic, the heat that is turbulently diffused into the gyre interior is subsequently brought closer to the surface by upwelling. Upwelling is thus an important yet poorly understood feature of the dynamics of the Weddell Gyre. This study marks the beginnings of a project focused on improved understanding of the role of upwelling within the Weddell Gyre, and investigating the role of turbulent diffusion in redistributing heat towards the central gyre interior, as well as towards the ice shelves of Antarctica.

How to cite: Reeve, K., Kanzow, T., Hoppema, M., Boebel, O., Strass, V., Geibert, W., and Gerdes, R.: The horizontal circulation, upwelling and heat budget of the Weddell Gyre: an observation perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16776, https://doi.org/10.5194/egusphere-egu2020-16776, 2020.

EGU2020-17529 | Displays | CR1.3

Initial results from International Thwaites Glacier Collaboration cruise NBP20-02

Robert Larter, Julia Wellner, Alastair Graham, Claus-Dieter Hillenbrand, Kelly Hogan, Frank Nitsche, James Smith, Lars Boehme, Mark Barham, John Anderson, Rebecca Minzoni, Lauren Simkins, Karen Heywood, and Erin Pettit and the NBP20-02 Shipboard Scientific Party

Thwaites Glacier (TG) is more vulnerable to unstable retreat than any other part of the West Antarctic Ice Sheet. This is due to its upstream-dipping bed, the absence of a large ice shelf buttressing its flow and the deep bathymetric troughs that route relatively warm Circumpolar Deep Water (CDW) to its margin. Over the past 30 years the mass balance of TG has become increasingly negative, suggesting that unstable retreat may have already begun. The International Thwaites Glacier Collaboration (ITGC) is an initiative jointly funded by the US National Science Foundation and the Natural Environment Research Council in the UK to improve knowledge of the boundary conditions and drivers of change at TG in order improve projections of its future contribution to sea level. The ITGC is funding a range of projects that are conducting on-ice and marine research, and applying numerical models to utilize results in order to predict how the glacier will change and contribute to sea level over coming decades to centuries.

RV Nathaniel B Palmer cruise NBP20-02, taking place from January­ to March 2020, will be the second ITGC multi-disciplinary research cruise, building on results from NBP19-02, which took place last year. Thwaites Offshore Research Project (THOR) aims during NBP20-02 include: extending the bathymetric survey in front of TG, collecting sediment cores at sites selected from the survey data, and acquiring high-resolution seismic profiles to determine the properties of the former bed of TG that is now exposed. The detailed bathymetric data will reveal the dimensions and routing of troughs that conduct CDW to the glacier front and will image seabed landforms that provide information about past ice flow and processes at the bed when TG was more extensive. The sediment cores, together with ones collected recently beneath the ice shelf via hot-water drilled holes, will be analysed to establish a history of TG retreat, subglacial meltwater release, and CDW incursions extending back over decades, centuries and millennia before the short instrumental record. Thwaites-Amundsen Regional Survey and Network Project (TARSAN) researchers will reach islands and ice floes via zodiac boats to attach satellite data relay loggers to Elephant and Weddell seals. The loggers record ocean temperature and salinity during the seals’ dives, greatly increasing the spatial extent and time span of oceanographic observations. In addition to work that is part of the THOR and TARSAN projects, another cruise objective is to recover and redeploy long-term oceanographic moorings in the Amundsen Sea. We will present initial results from NBP20-02.

How to cite: Larter, R., Wellner, J., Graham, A., Hillenbrand, C.-D., Hogan, K., Nitsche, F., Smith, J., Boehme, L., Barham, M., Anderson, J., Minzoni, R., Simkins, L., Heywood, K., and Pettit, E. and the NBP20-02 Shipboard Scientific Party: Initial results from International Thwaites Glacier Collaboration cruise NBP20-02, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17529, https://doi.org/10.5194/egusphere-egu2020-17529, 2020.

EGU2020-10790 | Displays | CR1.3

Early detection of the Weddell polynya re-opening using SAR imagery

Adriano Lemos and Céline Heuzé

The sea ice thickness in the Weddell Sea during the austral winter normally exceeds 1 m, but in the case of a polynya, this thickness decreases to 10 cm or less. There are two theories as to why the Weddell Polynya opens: 1) comparatively warm oceanic water upwelling from its nominal depth of several hundred metres to the surface where it melts the sea ice from underneath; or 2) opening of a lead by a passing storm, lead which will then be maintained open either by the atmosphere or ocean and grow. The objective of this study is to estimate how long in advance the recent Weddell Polynya opening could have been detected by synthetic aperture radar (SAR) images due to the decrease of the sea ice thickness and/or early appearance of leads. We use high temporal and spatial resolution SAR images from the Sentinel-1 constellation (C-band) and ALOS2 (L-band) during the austral winters 2014-2018. We use an adapted version of the algorithm developed by Aldenhoff et al. (2018) to monitor changes in sea ice thickness over the polynya region. The algorithm detects the transition of the sea ice thickness through changes in small scale surface roughness and thus reduced backscatter, and allowing us to distinguish three different categories: ice, thin ice, and open water. The transition from ice to thin ice and then to open water indicates that the polynya is melted from under, whereas a direct transition from ice to open water will reveal leads. The high resolution and good coverage of the SAR imagery, and a combined effort of different satellites sensors (e.g. infrared and microwave sensors), opens the possibility of an early detection of Weddell Polynya opening.

How to cite: Lemos, A. and Heuzé, C.: Early detection of the Weddell polynya re-opening using SAR imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10790, https://doi.org/10.5194/egusphere-egu2020-10790, 2020.

EGU2020-19603 | Displays | CR1.3

Two ice shelf populations revealed in new gravity- derived bathymetry for the Thwaites, Crosson and Dotson ice shelves

Tom Jordan, David Porter, Kirsty Tinto, Romain Millan, Atsuhiro Muto, Kelly Hogan, Robert Larter, Alastair Graham, and John Paden

Ice shelf buttressing plays a critical role in the long-term stability of ice sheets. The underlying bathymetry and cavity thickness therefore is a key to accurate models of future ice sheet evolution. However, direct observation of sub-ice shelf bathymetry is time consuming, logistically risky, and in some areas simply not possible, meaning there is a blind-spot in our understanding of this key system. Here we use airborne gravity anomaly data to provide new estimates of sub-ice shelf bathymetry outboard of the rapidly changing West Antarctic Thwaites Glacier, and beneath the adjacent Dotson and Crosson Ice Shelves. These regions are of especial interest as the low-lying inland reverse slope of the Thwaites glacier system makes it vulnerable to collapse through marine ice sheet instability, with rapid grounding-line retreat observed since 1993 suggesting this process may be underway. Our results confirm a major marine channel > 800 m deep extends to the front of Thwaites Glacier, while the adjacent ice shelves are underlain by more complex bathymetry. Comparison of our new bathymetry with ice shelf draft reveals that ice shelves formed since 1993 comprise a distinct population where the draft conforms closely to the underlying bathymetry, unlike the older ice shelves which show a more uniform depth of the ice base. This indicates that despite rapid basal melting in some areas, these “new” ice shelves are not yet in equilibrium with the underlying ocean system. We propose qualitative models of how this transient ice-shelf configuration may have developed, but further investigation is required to constrain the longevity and full impact of these newly recognised systems.

How to cite: Jordan, T., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R., Graham, A., and Paden, J.: Two ice shelf populations revealed in new gravity- derived bathymetry for the Thwaites, Crosson and Dotson ice shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19603, https://doi.org/10.5194/egusphere-egu2020-19603, 2020.

EGU2020-1331 | Displays | CR1.3

Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements

Erin Pettit, Atsu Muto, Christian Wild, Karen Alley, Ted Scambos, Bruce Wallin, Martin Truffer, and Dale Pomraning

As part of the International Thwaites Glacier Collaboration (ITGC) field activity in West Antarctica for the 2019-2020 season, the Thwaites-Amundsen Regional Survey and Network (TARSAN) team drilled boreholes using hot water, deployed long-term instruments, and gathered several ground-based geophysical data sets to assess the ice-shelf stability and evolution.

The Thwaites Eastern Ice Shelf is an important buttress for a broad (25 km) section of Thwaites Glacier outflow and is restrained at present by a few pinning points at the northwestern edge of the shelf. The grounding line of this buttress has retreated within the last 5 years indicating instability. Recent imagery shows major new rifting and shearing within the ice shelf.

In the Dotson-Crosson Ice Shelf (a single ice shelf with a rapidly evolving central region that has thinned and ungrounded over the past 80 years), satellite data show significant ice flow speed and direction changes, as well as retreating grounding lines where tributary glaciers start to float and where ice flows over and around isolated bedrock pinning points. A complex geometry of deep seafloor troughs underlie the central ice-shelf area which lies at the convergence of the two major troughs that extend to the continental shelf edge at two widely separated locations (roughly 103°W and 117°W longitude along the continental shelf break).

We surveyed the central Thwaites Eastern Ice Shelf (‘Cavity Camp’, 75.05°S, 105.58°W) and central Dotson-Crosson Ice Shelf (`Upper Dotson’, 74.87°S, 112.20°W) to the extent possible considering site safety and scientific interest. Cavity Camp is located approximately 17 km down-flow of the 2011 Thwaites Glacier grounding line. Ground-penetrating radar data show the ice thickness near Cavity Camp to be 300m, which is ~200m thinner than in 2007 estimated from hydrostatic assumption using altimetry analysis by other researchers. The seafloor below Cavity Camp is 816m, based on pressure from a CTD profile (a ~540 m water column and ~40m of firn).   

Across the central Dotson-Crosson Ice Shelf, a network of basal channels creates variable thinning rates from near-zero to over 30 m/yr (estimated in several previous remote-sensing-based studies). Ice thickness near our camp over a subglacial channel is 390m and the ice has been thinning at ~25 m/yr estimated from satellite data. Seafloor elevation at the Dotson site is estimated at -570 m, but seismic surveys suggest that the seabed topography varies considerably beneath Dotson. 

On each ice shelf, we conducted ~200 km of multi-frequency ground-penetrating radar profiles. We also conducted 46 (Thwaites) and 17 (Dotson) autonomous phase-tracking radio echo-sounding (ApRES) repeat point measurements, as well as 37 (Thwaites) and more than 20 (Dotson) active-seismic spot soundings to characterize the sub-ice-shelf cavity shape, thinning rates, basal ice structures, and ocean circulation. We deployed two Automated Meteorology Ice Geophysics Ocean observation Systems (AMIGOS-III stations) on the Thwaites Ice Shelf that include a suite of surface sensors, a fiber-optic-based thermal profiler, and an ocean mooring. Additionally, we deployed four long-term ApRES on the two ice shelves to monitor temporal variability in ice melt.

How to cite: Pettit, E., Muto, A., Wild, C., Alley, K., Scambos, T., Wallin, B., Truffer, M., and Pomraning, D.: Thwaites and Dotson Ice Shelves: Field Site Selection and Early Results of Field Measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1331, https://doi.org/10.5194/egusphere-egu2020-1331, 2020.

EGU2020-12441 | Displays | CR1.3

Large-Scale Atmospheric Drivers of Snowfall on Thwaites Glacier

Michelle Maclennan and Jan Lenaerts

High snowfall events on Thwaites Glacier are a key influencer of its ice mass change. In this study, we diagnose the mechanisms for orographic precipitation on Thwaites Glacier by analyzing the atmospheric conditions that lead to high snowfall events. A high-resolution regional climate model, RACMO2, is used in conjunction with MERRA-2 and ERA5 reanalysis to map snowfall and associated atmospheric conditions over the Amundsen Sea Embayment. We examine these conditions during high snowfall events over Thwaites Glacier to characterize the drivers of the precipitation and their spatial and temporal variability. Then we examine the seasonal differences in the associated weather patterns and their correlations with El Nino Southern Oscillation and the Southern Annular Mode. Understanding the large-scale atmospheric drivers of snowfall events allows us to recognize how these atmospheric drivers and consequent snowfall climatology will change in the future, which will ultimately improve predictions of accumulation on Thwaites Glacier.

How to cite: Maclennan, M. and Lenaerts, J.: Large-Scale Atmospheric Drivers of Snowfall on Thwaites Glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12441, https://doi.org/10.5194/egusphere-egu2020-12441, 2020.

CR1.5 – Permafrost in transition - future of permafrost ecosystems and consequences for climate feedback

EGU2020-22219 | Displays | CR1.5 | Highlight

Impacts of thermokarst on permafrost carbon losses and ecosystem services

Merritt Turetsky, Carolyn Gibson, and Catherine Dieleman

Permafrost thaw is altering northern ecosystems and the services they provide at scales ranging from local subsidence to global climate feedbacks. In organic-rich peatlands, thermokarst initiation and spread rates are increasing with rising mean annual air temperatures, changes in wildfire, and human land use. This presentation will outline empirical and modeling approaches to better understand the consequences of thermokarst in peatlands as well as other types of northern terrains on carbon cycling, wildlife, and other aspects of ecosystem services.  We are using fine scale datasets and remote sensing to map thermokarst coverage and expansion in both the Northwest Territories, Canada and interior Alaska. Using chronosequences and regional gradients, we are studying thermokarst impacts along gradients of time-since-thaw. Through a Permafrost Carbon Network synthesis, we developed conceptual and numerical models to understand how thermokarst development (formation, stabilization, re-accumulation of permafrost in some conditions) affects carbon storage and release. We are using a combination of empirical and modelled data to test hypotheses about climatic, ecological, and Quaternary controls on thermokarst rates and subsequent impacts on ecosystem services. We demonstrate that thermokarst in peat-rich landscapes are hotspots for permafrost carbon release primarily through methane emissions, have the potential to impact hunter movement and safety, and affect caribou habitat quality.

How to cite: Turetsky, M., Gibson, C., and Dieleman, C.: Impacts of thermokarst on permafrost carbon losses and ecosystem services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22219, https://doi.org/10.5194/egusphere-egu2020-22219, 2020.

EGU2020-4322 | Displays | CR1.5

Carbon cycle of permafrost transect: main terrestrial and hydrological ecosystems of Eastern Siberia

Trofim Maximov, Han Dolman, Ayumi Kotani, Per Anderson, Ayaal Maksimov, and Roman Petrov

Almost 65% of Siberian forests and 23% of tundra vegetation grow in permafrost zone. According to our estimate, carbon stocks in the soils of forest and tundra ecosystems of Yakutia (Eastern Siberia, Russia) amount to 17 billion tons (125.5 million hectares of forest and 37 million hectares of tundra in total) that is about 25% of total carbon resource in the forest soils of the Russian Federation.
This presentation is compiled from the results of many years time series investigations conducted on the study of carbon cycle in permafrost-dominated forests with different productivity and typical tundra and along Great Lena river basin including Aldan and Viluy tributaries. 
Seasonal photosynthesis maximum of forest canopy vegetation in dry years falls into June, and in humid ones – into July. During the growing season the woody plants of Yakutia uptake from 1.5 to 4.0 t C ha-1 season-1 depending on water provision. Night respiration is higher in dry and extremely dry years (10.9 and 16.1% respectively). The productive process of tree species in Eastern Siberia is limited by endogenous (stomatal conductance) and exogenous (provision with moisture and nutrients, nitrogen specifically) factors. The increase of an atmospheric precipitation after long 2-3 annual droughts accompanied with strong surge in photosynthetic activity of forest plants is almost 2.5 times. 
The temperature of soil is a key factor influencing soil respiration in the larch forests. Average soil respiration for the growing season comes to 6.9 kg C ha-1 day-1, which is a characteristic of Siberian forests. Annual average soil emission is 4.5±0.6 t C ha-1 yr-1.
As our multi-year studies showed, there is significant interannual NEE variation in the Central Yakutia larch forest, while in the Southern Yakutia  larch forest and tundra ecosystem variation is more smooth, because the climatic conditions in these zones (close to the mountain and sea)  are less changeable than in sharply continental Central Yakutia. 
According to our long-term eddy-correlation data, the annual uptake of carbon flux (NEE) in the high productivity larch forest of South eastern Yakutia, 60N – 2.43±0.23 t C ha-1 yr-1, in the moderate productivity larch forest of the Central Yakutia, 62N makes 2.12±0.34 t C ha-1 yr-1 and in the tundra zone, 70N – 0.75±0.14 t C ha-1 yr-1.
Interannual variation of carbon fluxes in permafrost forests in Northeastern Russia (Yakutia) makes 1.7-2.4 t C ha-1 yr-1 that results in the upper limit of annual sequestering capacity of 450-617 Mt C yr-1. In connection with climate warming there is a tendency of an increase in the volume of carbon sequestration by tundra and as opposed to decrease by forest ecosystem in the result of prolongation of the growing season and changing of plant successions.  This is also supported by changes in land use as well as by CO2 sequestration in the form of fertilizer. 
According our biogeochemical investigation annual flux of carbon from main in Eastern Siberia Lena river hydrological basin is almost 6.2 Mt C yr-1 including 28% at Aldan and 14% at Viluy rivers.

How to cite: Maximov, T., Dolman, H., Kotani, A., Anderson, P., Maksimov, A., and Petrov, R.: Carbon cycle of permafrost transect: main terrestrial and hydrological ecosystems of Eastern Siberia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4322, https://doi.org/10.5194/egusphere-egu2020-4322, 2020.

EGU2020-1445 | Displays | CR1.5

Climate change and the carbon cycle of frozen floodplains.

Ko van Huissteden, Kanayim Teshebaeva, Yuki Cheung, Hein Noorbergen, and Mark van Persie

Permafrost-affected river plains are highly diverse in discharge regime, floodplain morphology, channel forms, channel mobility and ecosystems. Frozen floodplains range from almost barren systems with high channel mobility, to extensive wetland areas with low channel mobility, abundant abandoned channels, back-swamps and shallow floodplain lakes. Floodplain processes are increasingly affected by climate-induced changes in river discharge and temperature regime: changes in the dates of freeze-up, break-up and spring floods, and changes in the discharge distribution throughout the year.

In permafrost floodplains, changes in flooding frequency, flood height and water temperature affect active layer thickness, subsidence and erosion processes. Data from the Northeast Siberian Berelegh river floodplain (a tributary to the Indigirka river) demonstrate that increasing spring flood height potentially causes permafrost thaw, soil subsidence and increase of the floodplain area. INSAR (interferometric synthetic aperture radar) data indicate that poorly drained areas in this region are affected by soil subsidence. Morphological evidence for subsidence of the river floodplain is abundant, and river-connected lakes show expansion features also seen in thaw lakes.

These floodplain wetland ecosystems are also affected by changes in the discharge regime and permafrost. On the one hand, floodplains are sites of active sedimentation of organic matter-rich sediments and sequestration of carbon. This carbon is derived from upstream erosion of permafrost and vegetation, and from autochthonous primary production. Nutrient supply by flood waters supports highly productive ecosystems with a comparatively large biomass.

On the other hand, these ecosystems also emit high amounts of CH4, which may be affected by flooding regime. In the example presented here, the CH4 emission from floodplain wetlands is about seven times higher that the emission from similar tundra wetlands outside the floodplain.

The dynamic nature of floodplains hinders carbon and greenhouse gas flux measurements. Better quantification of greenhouse gas fluxes from these floodplains, and their relation with river regime changes, is highly important to understand future emissions from thawing permafrost. Given the difficulties of surface greenhouse gas flux measurements, recent remote sensing material could play an important role here.

How to cite: van Huissteden, K., Teshebaeva, K., Cheung, Y., Noorbergen, H., and van Persie, M.: Climate change and the carbon cycle of frozen floodplains., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1445, https://doi.org/10.5194/egusphere-egu2020-1445, 2020.

EGU2020-6246 | Displays | CR1.5

Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau

Lin Zhao, Guojie Hu, Defu Zou, Ren Li, Yu Sheng, and Qiangqiang Pang

Due to the climate warming, permafrost on the Qinghai-Tibet Plateau (QTP) was degradating in the past decades. Since its impacts on East Asian monsoon, and even on the global climate system, it is fundamental to reveal permafrost status, changes and its physical processes. Based on previous research results and new observation data, this paper reviews the characteristics of the status of permafrost on the QTP, including the active layer thickness (ALT), the spatial distribution of permafrost, permafrost temperature and thickness, as well as the ground ice and soil carbon storage in permafrost region.

The results showed that the permafrost and seasonally frozen ground area (excluding glaciers and lakes) is 1.06 million square kilometters and 1.45 million square kilometters on the QTP. The permafrost thickness varies greatly among topography, with the maximum value in mountainous areas, which could be deeper than 200 m, while the minimum value in the flat areas and mountain valleys, which could be less than 60 m. The mean value of active layer thickness is about 2.3 m. Soil temperature at 0~10 cm, 10~40 cm, 40~100 cm, 100~200 cm increased at a rate of 0.439, 0.449, 0.396, and 0.259°C/10a, respectively, from 1980 to 2015. The increasing rate of the soil temperature at the bottom of active layer was 0.486 oC/10a from 2004 to 2018.

The volume of ground ice contained in permafrost on QTP is estimated up to 1.27×104 km3 (liquid water equivalent). The soil organic carbon staored in the upper 2 m of soils within the permafrost region is about 17 Pg. Most of the research results showed that the permafrost ecosystem is still a carbon sink at the present, but it might be shifted to a carbon source due to the loss of soil organic carbon along with permafrost degradation.

Overall, the plateau permafrost has undergone remarkable degradation during past decades, which are clearly proven by the increasing ALTs and ground temperature. Most of the permafrost on the QTP belongs to the unstable permafrost, meaning that permafrost over TPQ is very sensitive to climate warming. The permafrost interacts closely with water, soil, greenhouse gases emission and biosphere. Therefore, the permafrost degradation greatly affects the regional hydrology, ecology and even the global climate system.

How to cite: Zhao, L., Hu, G., Zou, D., Li, R., Sheng, Y., and Pang, Q.: Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6246, https://doi.org/10.5194/egusphere-egu2020-6246, 2020.

Mean annual temperatures in interior Alaska, currently -1°C, are projected to increase as much as 5°C by 2100. An increase in mean annual temperatures is expected to degrade permafrost and alter hydrogeology, soils, vegetation, and microbial communities. Ice and carbon rich “yedoma type” permafrost in the area is ecosystem protected against thaw by a cover of thick organic soils and mosses. As such, interactions between vegetation, permafrost ice content, the snow pack, and the soil thermal regime are critical in maintaining permafrost. We studied how and where vegetation and soil surface characteristics can be used to identify subsurface permafrost composition. Of particular interest were potential relationships between permafrost ice content, the soil thermal regime, and vegetation cover. We worked along 400-500 m transects at sites that represent the variety of ecotypes common in interior Alaska. Airborne LiDAR imagery was collected from May 9-11, 2014 with a spatial resolution of 0.25 m. During the winters from 2013-2019 snow pack depths have been made at roughly 1 m intervals along site transects using a snow depth datalogger coupled with a GPS. In late summer from 2013-2019 maximum seasonal thaw depths have been measured at 4 m intervals along each transect. Electrical resistivity tomography measurements were collected across the site transects. A variety of machine learning geospatial analysis approaches were also used to identify relationships between ecosystem characteristics, seasonal thaw, and permafrost soil and ice composition. Wintertime measurements show a clear relationship between vegetation cover and snow depth. Interception (and shallow snow) was evident in the birch and white spruce forests and where dense shrubs are present while the open tussock and intermittent shrub regions yield the greatest snow depths. Results from repeat seasonal thaw depth measurements also show a strong relationship with vegetation where mixed birch and spruce forest is associated with the deepest seasonal thaw. The tussock/shrub and spruce forest zones consistently exhibited the shallowest seasonal thaw. Roughly 60% of the seasonal thaw along the transects occurred by mid-July and downward movement of the thaw front had mostly ceased by late August with little additional thaw between August 20 and early October. Summer precipitation shows a relationship with seasonal thaw depth with the wettest summers associated with the deepest thaw. Results from this study identify clear relationships between ecotype, permafrost composition, and seasonal thaw dynamics that can help identify how and where permafrost degradation can be expected in a warmer future arctic.

How to cite: Douglas, T., Hiemstra, C., Anderson, J., and Zhang, C.: Identifying vegetation-geomorphology relationships in permafrost with airborne LiDAR, electrical resistivity tomography, seasonal thaw depth measurements, and machine learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1900, https://doi.org/10.5194/egusphere-egu2020-1900, 2020.

EGU2020-17416 | Displays | CR1.5 | Highlight

Siberian Arctic inland waters emit mostly contemporary carbon

Joshua Dean, Ove Meisel, Melanie Martyn Roscoe, Luca Belelli Marchesini, Mark Garnett, Henk Lenderink, Richard van Logtestijn, Alberto Borges, Steven Bouillon, Thibault Lambert, Thomas Röckmann, Trofim Maximov, Roman Petrov, Sergei Karsanaev, Rien Aerts, Jacobus van Huissteden, Jorien Vonk, and Han Dolman

Inland waters (rivers, lakes and ponds) are important conduits for the emission of terrestrial carbon in Arctic permafrost landscapes. These emissions are driven by turnover of contemporary terrestrial carbon and additional “pre-aged” (Holocene and late-Pleistocene) carbon released from thawing permafrost soils, but the magnitude of these source contributions to total inland water carbon fluxes remains unknown. Here we present unique simultaneous radiocarbon age measurements of inland water CO2, CH4 and dissolved and particulate organic carbon in northeast Siberia during summer. We show that >80% of total inland water carbon emissions were contemporary in age, but that pre-aged carbon contributed >50% at sites strongly affected by permafrost thaw. CO2 and CH4 were younger than dissolved and particulate organic carbon, suggesting emissions were primarily fuelled by contemporary carbon decomposition. The study region was a net carbon sink (-876.9 ± 136.4 Mg C for 25 July to 17 August), but inland waters were a source of contemporary (16.8 Mg C) and pre-aged (3.7 Mg C) emissions that respectively offset 1.9 ± 1.2% and 0.4 ± 0.3% of CO2 uptake by tundra (‑897 ± 115 Mg C). Our findings reveal that inland water carbon emissions from permafrost landscapes may be more sensitive to changes in contemporary carbon turnover than the release of pre-aged carbon from thawing permafrost.

How to cite: Dean, J., Meisel, O., Martyn Roscoe, M., Belelli Marchesini, L., Garnett, M., Lenderink, H., van Logtestijn, R., Borges, A., Bouillon, S., Lambert, T., Röckmann, T., Maximov, T., Petrov, R., Karsanaev, S., Aerts, R., van Huissteden, J., Vonk, J., and Dolman, H.: Siberian Arctic inland waters emit mostly contemporary carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17416, https://doi.org/10.5194/egusphere-egu2020-17416, 2020.

EGU2020-1465 | Displays | CR1.5

Organic carbon sorbed to reactive iron minerals released during permafrost collapse

Monique S. Patzner, Merritt Logan, Carsten W. Mueller, Hanna Joss, Sara E. Anthony, Thomas Scholten, James M. Byrne, Thomas Borch, Andreas Kappler, and Casey Bryce

The release of vast amounts of organic carbon during thawing of high-latitude permafrost is an urgent issue of global concern, yet it is unclear what controls how much carbon will be released and how fast it will be subsequently metabolized and emitted as greenhouse gases. Binding of organic carbon by iron(III) oxyhydroxide minerals can prevent carbon mobilization and degradation. This “rusty carbon sink” has already been suggested to protect organic carbon in soils overlying intact permafrost. However, the extent to which iron-bound carbon will be mobilized during permafrost thaw is entirely unknown. We have followed the dynamic interactions between iron and carbon across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost retreat. Using both bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS), we found that up to 19.4±0.7% of total organic carbon is associated with reactive iron minerals in palsa underlain by intact permafrost. However, during permafrost collapse, the rusty carbon sink is lost due to more reduced conditions which favour microbial Fe(III) mineral dissolution. This leads to high dissolved Fe(II) (2.93±0.42 mM) and organic carbon concentrations (480.06±34.10 mg/L) in the porewater at the transition of desiccating palsa to waterlogged bog. Additionally, by combining FT-ICR-MS and greenhouse gas analysis both in the field and in laboratory microcosm experiments, we are currently determining the fate of the mobilized organic carbon directly after permafrost collapse. Our findings will improve our understanding of the processes controlling organic carbon turnover in thawing permafrost soils and help to better predict future greenhouse gas emissions.

 

How to cite: Patzner, M. S., Logan, M., Mueller, C. W., Joss, H., Anthony, S. E., Scholten, T., Byrne, J. M., Borch, T., Kappler, A., and Bryce, C.: Organic carbon sorbed to reactive iron minerals released during permafrost collapse , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1465, https://doi.org/10.5194/egusphere-egu2020-1465, 2020.

EGU2020-1431 | Displays | CR1.5

SourcE and impact of greeNhousE gasses in AntarctiCA: the Seneca project

Livio Ruggiero, Alessandra Sciarra, Adriano Mazzini, Claudio Mazzoli, Valentina Romano, Maria Chiara Tartarello, Fabio Florindo, Massimiliano Ascani, Gary Wilson, Bob Dagg, Richard Hardie, Jacob Anderson, Rachel Worthington, Matteo Lupi, Sabina Bigi, Giancarlo Ciotoli, Stefano Graziani, Federico Fischanger, and Raffaele Sassi

Current global climate changes represent a threat for the stability of the polar regions and may result in cascading broad impacts. Studies conducted on permafrost in the Arctic regions indicate that these areas may store almost twice the carbon currently present in the atmosphere. Therefore, permafrost thawing may potentially cause a significant increase of greenhouse gases concentrations in the atmosphere, exponentially rising the global warming effect. Although several studies have been carried out in the Arctic regions, there is a paucity of data available from the Southern Hemisphere. The Seneca project aims to fill this gap and to provide a first degree of evaluations of gas concentrations and emissions from permafrost and/or thawed shallow strata of the Dry Valleys in Antarctica. The Taylor and Wright Dry Valleys represent one of the few Antarctic areas that are not covered by ice and therefore represent an ideal target for permafrost investigations.

Here we present the preliminary results of a multidisciplinary field expedition conducted during the Antarctic summer in the Dry Valleys, aimed to collect and analyse soil gas and water samples, to measure CO2 and CH4 flux exhalation, to investigate the petrological soil properties, and to acquire geoelectrical profiles. The obtained data are used to 1) derive a first total emission estimate for methane and carbon dioxide in this part of the Southern Polar Hemisphere, 2) locate the potential presence of geological discontinuities that can act as preferential gas pathways for fluids release, and 3) investigate the mechanisms of gas migration through the shallow sediments. These results represent a benchmark for measurements in these climate sensitive regions where little or no data are today available.

How to cite: Ruggiero, L., Sciarra, A., Mazzini, A., Mazzoli, C., Romano, V., Tartarello, M. C., Florindo, F., Ascani, M., Wilson, G., Dagg, B., Hardie, R., Anderson, J., Worthington, R., Lupi, M., Bigi, S., Ciotoli, G., Graziani, S., Fischanger, F., and Sassi, R.: SourcE and impact of greeNhousE gasses in AntarctiCA: the Seneca project , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1431, https://doi.org/10.5194/egusphere-egu2020-1431, 2020.

Ice wedge (IW) polygons form through thermal contraction induced by winter cooling of ice-rich permafrost which results in the formation of cracks. Hoar frost develops in the cracks in winter and meltwater infills the cracks during spring and freezes. As the cracking and infilling occurs repeatedly, IWs grow, leading to characteristic surface morphology with depressions or troughs aligned on the axis of the IW and raised rims or ridges on either side. Surface expression of IW is either characterized as low-centered polygons or high-centered polygons, the former being associated with the first stages of IW development, and the latter with IW degradation. Because IWs represent important excess ice close to the surface, considerable local subsidence and related effects on landscape parameters, such as vegetation and moisture, are likely to occur upon degradation.

IW polygons distribution, morphometry and state were characterized in the Tombstone Territorial Park (Central Yukon, Canada) using semi-automated remote sensing techniques, field observations and laboratory analyses. The data is used to define determining landscape factors for IW polygons occurrence, to characterise the stages of the IWs development and/or degradation and to estimate the volume of buried ice in the region. Results show that elevation, slope and material are important elements defining IW polygons distribution. The relationship between landscape factors and stages of development is not as clear, and, despite climate changes being homogenous in the area, IW development and degradation is very heterogenous, as shown by the differing moisture, greenness and brightness signals across the polygonal terrain.

How to cite: Frappier, R. and Lacelle, D.: Ice-wedge polygons distribution, morphometry and state in the Tombstone Territorial Park, Central Yukon, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12044, https://doi.org/10.5194/egusphere-egu2020-12044, 2020.

EGU2020-3859 | Displays | CR1.5

Global climate warming: permafrost degradation and expected consequences

Maria Romanovskaya, Vladimir Romanovsky, and Tatiana Kuznetsova

At present, the degradation of permafrost caused by climate warming raises serious concerns of scientists and the public around the world. As a result of degradation of permafrost containing a huge amount of organic material and the decomposition of this organic material, the greenhouse effect can increase significantly. Some scientists estimate that the amount of carbon in the permafrost is more than two times than there is in atmospheric carbon dioxide (Schuur E. A. G.et al., 2015).  Besides, a large amount of greenhouse gasses, mostly methane, is already contained in watery glacier bottoms, where these gasses build up through anaerobic organic decomposition (Burns R., 2018). Therefore, there are concerns that permafrost thaw and glacier retreat as the Earth warms will lead to new greenhouse gasses being released into the atmosphere, thus further accelerating the global warming process. 
Our research devoted to this problem was carried out at the archaeological Upper Paleolithic site Divnogorie 9 (50.9649° N, 39.3031° E) in the National Park “Divnogorie”. Our study area occupies the southern part of the Middle Russian Upland (the East European Plain). It has experienced several Quaternary glaciations: the Don, Dnepr, Moscow, and Valdai Glaciations. The facts of the presence of permafrost and its degradation during the late Pleistocene and Holocene are established here as well. The site is located at the right bank of the Tikhaya Sosna River, a right tributary of the Don River. The Don River basin is a world known area because of high concentration of the Upper Paleolithic archaeological sites here - Kostenki-Borshevo district (51°23'40'' N, 39º30'31''E) which contains 26 open-air mammoth remnant sites (38-18 ka BP). 
Divnogorie 9 is an unique site in Europe which is well-known for numerous findings of fossilized equestrian remains of wild horses - more than eight thousands samples. Our most detailed study of the Quaternary deposits was carried out at a 18-m thick section. Bones are concentrated in seven layers (levels). This section exposes several paleosol layers, as well. Estimates of the radiocarbon age of the fossils and paleosol layers here yielded 14-12 ka BP. We studied the organic carbon from paleo-soils of Divnogorie 9. The abundant presence of such large grazers as horses and especially mammoths during the Late Pleistocene supports the widespread existence of high productivity grasslands and organic-rich soils. 
However, the results of our analysis do not show a significant amount of organic carbon in these paleo-soils at the present. It may possibly be an indication that the originally carbon rich permafrost and subglacial deposits lost their carbon upon permafrost thaw and glacial retreat during the transition from the last glaciation to the Holocene. This ancient carbon was massively released into the atmosphere and to the aquatic systems during that time. At the same time, there were not widespread catastrophic consequences to the Earth’s environment except possibly for the extinction of mammoths and other large fauna in the arctic and subarctic. These results provide some cautious optimism about the severity in current amount of changes and consequences thereof. 

How to cite: Romanovskaya, M., Romanovsky, V., and Kuznetsova, T.: Global climate warming: permafrost degradation and expected consequences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3859, https://doi.org/10.5194/egusphere-egu2020-3859, 2020.

EGU2020-7727 | Displays | CR1.5

Arctic greening, Arctic browning or Arctic drowning?

Rúna Magnússon, Monique M. P. D. Heijmans, Juul Limpens, Ko van Huissteden, David Kleijn, and Trofim C. Maximov

Thawing of permafrost and the resulting decomposition of previously frozen organic matter constitute a positive feedback to global climate. However, contrasting mechanisms are at play. Gradual increases in thawing depth and temperature are associated with enhanced vegetation growth, most notably in shrubs (“greening”). In ice-rich permafrost, abrupt thaw (thermokarst) results in disturbance of vegetation and surface wetting, which may result in an opposing trend (“browning”).

We determined the balance of shrub decline and expansion in an ice-rich lowland tundra ecosystem in north-Eastern Siberia using vegetation classification and change analysis. We used random forest classification on 3 very high resolution commercial satellite images gathered between 2010 and 2019 (GeoEye-I and WorldView-II). To mitigate (slight) differences in sensor properties and vegetation phenology, a spatio-temporal implementation of Potts model was used to utilize both spectral properties of a pixel and its degree of correspondence with spatially and temporally neighbouring pixels. This reduced artefacts in change detection substantially and improved accuracy of classification for all three images.

We found that shrub vegetation declines in this lowland tundra ecosystem. Areas of thaw features (thermokarst ponds, thermoerosion gullies) and aquatic plant types (sedges and peat mosses) however show an increasing trend. Markov Chain analysis reveals that thaw features display a succession from open water / mud to sedges to peat moss. 

This transition from shrub dominated to wetland species dominated tundra may have important implications for this ecosystem's greenhouse gas balance and is indicative of wetter conditions. Thermokarst may be an important driver of such change, as thaw features are found to expand at the expense of shrub vegetation and show rapid colonization by aquatic species. 

How to cite: Magnússon, R., Heijmans, M. M. P. D., Limpens, J., van Huissteden, K., Kleijn, D., and Maximov, T. C.: Arctic greening, Arctic browning or Arctic drowning?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7727, https://doi.org/10.5194/egusphere-egu2020-7727, 2020.

EGU2020-5404 | Displays | CR1.5

What governs the effects of permafrost thaw on boreal forest dynamics?

Aleksandra Kulawska, Thomas A. M. Pugh, Nicholas Kettridge, Rob MacKenzie, and Sami Ullah

Boreal forests are located at latitudes that are predicted to experience some of the greatest warming on the planet. Forests growing on permafrost may be particularly vulnerable, with accelerated soil warming and permafrost degradation linked to changing patterns of tree growth and longevity. Many have speculated that thawing permafrost, through its effects on soil water content and ground stability, will increase forest mortality across the boreal region. However, recent evidence indicates mixed forest responses to permafrost thaw. In some areas, the onset of thaw is followed by increased tree growth and increased forest cover area. In other sites, thaw has been linked to decreased growth and forest cover loss. It is currently poorly understood what determines these contrasting responses, and the roles that different environmental and climatic factors may play. This leads to two major issues: (1) uncertainties in predicting the effects of future permafrost thaw on carbon dynamics in northern ecosystems, and (2) poor understanding of where scientific and conservation efforts should be focused. Here, we present a review of the recent evidence of permafrost thaw effects on boreal forest dynamics and propose an explanation for the differing responses across sites. We argue that the outcome is controlled by a set of factors that influence two major pathways and the interactions between them: (1) permafrost-soil water content and (2) soil water content-plant growth. We present a series of conceptual models explaining these interactions and highlight the largest sources of uncertainties. Based on these, we propose a set of hypotheses and methodologies to guide future research in this area.

How to cite: Kulawska, A., Pugh, T. A. M., Kettridge, N., MacKenzie, R., and Ullah, S.: What governs the effects of permafrost thaw on boreal forest dynamics? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5404, https://doi.org/10.5194/egusphere-egu2020-5404, 2020.

Model projections of CO2 and CH4 exchange in Arctic tundra during the next century diverge widely.  In this modelling study, we used ecosys to examine how climate change will affect CO2 and CH4 exchange through its effects on net primary productivity (NPP), heterotrophic respiration (Rh) and thereby on net ecosystem productivity (NEP) in landform features (troughs, rims, centers) of a coastal polygonal tundra landscape at Barrow AK. The model was shown to simulate diurnal and seasonal variation in CO2 and CH4 fluxes associated with those in air and soil temperatures (Ta and Ts) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising Ta, atmospheric CO2 concentrations (Ca) and precipitation  (P) increased NPP from 50 – 150 g C m-2 y-1,  consistent with current biometric estimates, to 200 – 250 g C m-2 y-1, depending on feature elevation. Concurrent increases in Rh were slightly smaller, so that net CO2 exchange rose from values of -25 (net emission) to +50 (net uptake) g C m-2 y-1 to ones of -10 to +65 g C m-2 y-1, again depending on feature elevation. Large increases in Rh with thawing permafrost were not modelled. Increases in net CO2 uptake were largely offset by increases in CH4 emissions from 0 – 6 g C m-2 y-1 to 1 – 20 g C m-2 y-1, depending on feature elevation, reducing gains in NEP. Increases in CH4 emissions with climate change were mostly attributed to increases in Ta, but also to increases in Ca and P. These increases in net CO2 uptake and CH4 emissions were modelled with hydrological boundary conditions that were assumed not to change with climate.  Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change. The model was then applied to the entire permafrost zone of North America to project RCP 8.5 climate change effects on active layer depth and ecosystem productivity by 2100.  

How to cite: Grant, R.: Climate change impacts on CO2 and CH4 exchange in an Arctic polygonal tundra depend on changes in vegetation and drainage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2027, https://doi.org/10.5194/egusphere-egu2020-2027, 2020.

EGU2020-9279 | Displays | CR1.5

Landscape Controls on the Hydrological Variability of Thermokarst Lakes between Inuvik and Tuktoyaktuk, NWT

Evan J. Wilcox, Branden Walker, Gabriel Hould - Gosselin, Oliver Sonnentag, Brent B. Wolfe, and Philip Marsh

The Arctic is warming at twice the rate of the rest of the world, causing precipitation to shift from snowfall to rainfall, permafrost to thaw, longer snow-free land and ice-free lakes, and increased evaporation. Thermokarst lakes across the Arctic have experienced different changes over the past decades: in some regions, lakes are expanding through thawing adjacent permafrost, while in other regions they are drying up and shrinking, or not changing at all. It is important to understand what governs lake water balance as it affects lake ecosystems that support large populations of migratory birds and fish; are important to local communities for food and recreation; and control the flux of carbon and other nutrients from thawing permafrost into lakes. For example, lake inflow, evaporation and water residence time affect the concentration of nutrients within lakes, ultimately affecting the aquatic ecosystem and greenhouse gas release. Previous research has focused on quantifying the water inputs and outputs of individual lakes, but a better understanding of the drivers and processes controlling lake water balances is required to understand how they will respond to a changing climate.

We measured lake water flux components at multiple spatial and temporal scales across the 5000 km2 boreal – tundra transition zone between Inuvik and Tuktoyaktuk, Northwest Territories, Canada. Lake water flux components were measured at two adjacent thermokarst lakes with different ratios of lake area to catchment area (LACA), from 2017 – 2019. Also, water isotope samples were collected from March – September 2018 from ~100 lakes across 2000 km2. From these water isotope compositions we estimated the ratio of evaporation to inflow, residence time, and the mixture of snowmelt and rainfall runoff in each lake. Catchments of all 7500 lakes in the region were delineated using a high-resolution digital elevation model in order to estimate their LACA, and evaluate connectivity between lakes.

Paired lake water balance measurements showed that the lake with a larger LACA had a residence time an order of magnitude shorter than the larger lake, and displayed larger fluctuations in water level. Also, the ratio of evaporation to inflow was significantly larger in lakes with smaller LACA. Water isotope compositions showed that only 10-50% of a lake’s water is replaced by snowmelt in spring, as the majority of snowmelt runoff flowed overtop of lake ice and through the lake outlet. Deeper lakes had significantly less snowmelt mixing, as the volume of water for the snowmelt to mix with was greater than in shallower lakes. These results show that lake water balance can be characterized using lake and catchment properties, allowing future research to more easily characterize lake hydrology and build further understanding about how lake water balance is connected to other aspects of the permafrost environment.

How to cite: Wilcox, E. J., Walker, B., Hould - Gosselin, G., Sonnentag, O., Wolfe, B. B., and Marsh, P.: Landscape Controls on the Hydrological Variability of Thermokarst Lakes between Inuvik and Tuktoyaktuk, NWT , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9279, https://doi.org/10.5194/egusphere-egu2020-9279, 2020.

EGU2020-1740 | Displays | CR1.5

Solar Radiation Modification Slows Down Permafrost Carbon Loss

Yangxin Chen and Duoying Ji

    Circumpolar permafrost is degrading under anthropogenic global warming, thus the large amount of soil organic carbon in it would be vulnerable to microbial decomposition and further aggravating future warming. However, solar radiation modification (SRM), as a theoretical approach to reducing some of the impacts of anthropogenic climate change, hopefully could mitigate the permafrost degradation and slow down permafrost carbon loss. Here we use two solar geoengineering experiments came up in CMIP6/GeoMIP6 -- G6solar and G6sulfur, to explore changes in circumpolar permafrost carbon under solar radiation modification scenarios. Earth system models' simulations show that under G6 scenarios, annual mean surface air temperature in circumpolar permafrost region is about 5℃ lower relative to the high forcing scenario SSP5-8.5 by year 2100, with a growing trend but remains below 0℃ from 2015 to 2100, which is close to that in the medium forcing scenario SSP2-4.5. The lower temperature causes lower degradation rate of permafrost area. In SSP5-8.5 scenario, almost all the permafrost thaws by year 2100, but up to half of it remains frozen in SSP2-4.5 and G6 scenarios compared to year 2015. The lower temperature also results in less carbon assimilation in this area, thus the lower vegetation carbon accumulation. By 2100, a maximum soil carbon loss of 18.09 PgC under SSP5-8.5 scenario regarding to different model constructions, while in G6 the soil carbon loss could be reduce to 3.70 PgC, even less than that of 5.29 PgC in SSP2-4.5 scenario.

How to cite: Chen, Y. and Ji, D.: Solar Radiation Modification Slows Down Permafrost Carbon Loss , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1740, https://doi.org/10.5194/egusphere-egu2020-1740, 2020.

EGU2020-19337 | Displays | CR1.5

The carbon budget of a tundra in the north-eastern Russian Arctic during the snow free season and its stability in the 2003-2016 period

Han Dolman, Jacobus van Huissteden, Joshua Dean, Trofim Maximov, Roman Petrov, and Luca Belelli Marchesini

Large quantities of carbon are stored in the terrestrial permafrost of the Arctic region where the rate of climate warming is two to three times more than the global mean and the largest temperature anomalies observed in autumn and winter. The quantification of the impact of climate warming on the degradation of permafrost and the associated potential release to the atmosphere of carbon stocked in the soil in the form of greenhouse gases, thus further increasing the radiative forcing of the atmosphere, is a research priority in the field of biogeosciences. Land-atmosphere turbulent fluxes of CO2 and CH4 have been monitored at the tundra site of Kytalyk in north-eastern Siberia (70,82 N; 147.48 E) by means of eddy covariance since 2003 and 2008, respectively; regular measurement campaigns have been carried out since then. Here we present results of the seasonal CO2 budget of the tundra ecosystem for the 2003-2016 period based on observations encompassing the permafrost thawing season and analyze the inter-annual differences in the seasonal patterns of CO2 fluxes considering the separate the contribution of climatic drivers and ecosystem functional parameters relative to the processes of respiration and photosynthesis. The variability of the CO2 budget is also discussed in view of the impact of the timing and length of the snow free period.

The Kytalyk tundra acted as an atmospheric carbon dioxide sink with relatively small inter-annual variability (-96.1±11.9 gC m-2) during the snow free season and the seasonal CO2 budget did not show any trend over time. The pronounced meteorological variability characterizing Arctic summers was a key factor in shaping the length of the carbon uptake period, which did not progressively increased despite its tendency to start earlier, and in determining the magnitude of CO2 fluxes. No clear evidence of inter-annual changes in the eco-physiological response parameters of CO2 fluxes to climatic drivers (global radiation and air temperature) was found along the course of the analysed period. Methane fluxes had a minor contribution to the carbon budget of the snow-free season representing on average an emission of 3.2 gC m-2 (2008-2016) with apparently small inter-annual variability. Similarly, the size of the carbon exported laterally from the ecosystem in the form of dissolved organic carbon flux amounted to 3.1 gC m-2 as determined experimentally. After including these last terms in the budget, the magnitude of the carbon sink associated with the net ecosystem productivity is reduced by 6%, while the GHG budget still denotes a sink of -60.4 ± 11.9 gC-CO2eq (methane GWP over 100-year time horizon).

The monitored tundra was to date exerting a steady climate warming mitigation effect as far as the snow free season is concerned, however the figure of its carbon sink could be potentially sensibly lower due to overlooked emissions in the autumn freeze-up and early winter periods. Also, nonlinear accelerations in the permafrost degradation could happen once tipping points in the Arctic climate are exceeded. Both aspects underline the relevance of long term and continuous biogeochemical monitoring in permafrost tundra environments.

How to cite: Dolman, H., van Huissteden, J., Dean, J., Maximov, T., Petrov, R., and Belelli Marchesini, L.: The carbon budget of a tundra in the north-eastern Russian Arctic during the snow free season and its stability in the 2003-2016 period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19337, https://doi.org/10.5194/egusphere-egu2020-19337, 2020.

EGU2020-5988 | Displays | CR1.5

Overlooked volatile production from Arctic permafrost triggered by global warming

Haiyan Li, Mari Mäki, Lukas Kohl, Minna Väliranta, Jaana Bäck, and Federico Bianchi

Permafrost thaw, as a consequence of climate warming, liberates large quantities of frozen organic carbon in the Arctic regions. The response of gaseous carbon release upon permafrost thaw might play a crucial role in the future evolution of atmosphere-land fluxes of biogenic gases such as volatile organic compounds (VOCs), a group of reactive gases and the dominant modulator of tropospheric oxidation capacities. Here, we examine the response of volatile release from Finnish Lapland permafrost soils to temperature increase in a series of laboratory incubation experiments. The experiments show that when the temperature rises from 0 °C to 15 °C, various VOC species are significantly emitted from the gradually thawing soils. The VOC fluxes from thawing permafrost are on average four times as high as those from active layer. Acetic acid and acetone dominate the total volatile emissions from both permafrost and active layer, with significant amounts of aromatics and terpenes detected as well. The emission rate and the composition of volatile release from thawing soils are highly responsive to temperature variations. As temperature increases, more less volatile compounds are released, i.e., sesquiterpenes and diterpenes. Collectively, these results demonstrate the highly overlooked volatile production from thawing permafrost, which will create a stronger permafrost carbon-climate feedback.

How to cite: Li, H., Mäki, M., Kohl, L., Väliranta, M., Bäck, J., and Bianchi, F.: Overlooked volatile production from Arctic permafrost triggered by global warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5988, https://doi.org/10.5194/egusphere-egu2020-5988, 2020.

The Arctic permafrost soils are very diverse in regard to parent material, geobiological composition and genesis. There is sparse knowledge about nutrient availability in Arctic soil and it was found that the permafrost layer differs in nutrient availability compared to the active layer. Recently, it was shown that elements like Si, Ca and P are potentially affecting the greenhouse gas from Arctic soil. However, it is not known how those elements are distributed in Arctic soils for a larger dataset. Furthermore, it is unclear whether regional differences in the availability of those elements or a change in availability due to permafrost thaw is changing microbial decomposer community. Therefore, we analyzed 445 soil depth profiles around the Arctic regarding different element availabilities.

Furthermore, we conducted an incubation experiment to measure the effect of different Si, Ca and P availabilities on the structure of the microbial decomposer community. We found large differences in the availability of Si, Ca, Al, Fe and P in the layers of the panarctic permafrost soils from Canada, Alaska, Russia, Scandinavia, Greenland and Svalbard. There are differences in the distribution of Ca and Si pools over the panarctic permafrost soils. Especially the availability of P is directly linked to the concentration of Ca and Si and the presence of Al and Fe based minerals. With rising temperatures, the thaw depth of the upper horizon may increase and elements stored in deeper layers become potentially mobilized. These processes modify the nutrient availability for microorganisms and by this the production of greenhouse gases like CO2 and CH4.

The community structure of bacteria and fungi is related to the availability of Ca and Si. With modified availabilities of Si and Ca, we found direct linear correlations in the changes of the microbial structure at the phylum level for Greenlandic soils. These changes depend on the origin of the soil and the original availability of Ca and Si. We found direct links between the share of gram-positive bacteria and the Ca concentration in both soils and the production of greenhouse gases. The availabilities of these elements may be helpful for better predicting greenhouse gases fluxes in the Arctic as well as element transfer to marine systems.

How to cite: Stimmler, P.: Future Arctic soil nutrient availability and microbial community structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6870, https://doi.org/10.5194/egusphere-egu2020-6870, 2020.

EGU2020-12521 | Displays | CR1.5

Nutrients unlocked from permafrost thaw affect microbial methane metabolism

Natalie N. Kashi, Ruth K. Varner, Nathan R. Thorp, Melissa A. Knorr, Adam S. Wymore, Jessica G. Ernakovich, Erik A. Hobbie, and Reiner Giesler

The biological conversion of frozen carbon-rich soil (permafrost) into greenhouse gases such as carbon dioxide could cause a positive feedback to climate change. Another significant consequence of permafrost thaw is the collapse of soil structure and subsequent higher water table that can shift vegetation toward water-adapted plant communities that emit high concentrations of methane (CH4). Plants and microbes respond rapidly to labile carbon (C) and nitrogen (N) released from permafrost thaw, however, the microbial response to phosphorus (P) is unknown.  Here we investigated how the nutrient status of permafrost and peat affect microbial activities in four minerotrophic communities in a peatland undergoing permafrost thaw. We experimentally fertilized soils in vitro with a permafrost soil slurry, inorganic P, organic N, or organic N and P. This method isolated the effect of permafrost thaw on microbial processes by removing the confounding effect of plant-soil interactions. The four peatland communities include 1. palsas (intact permafrost mounds rising above the surrounding peatlands), 2. pockets of collapsed palsas dominated by Sphagnum fuscum, 3. adjacent eutrophic Sphagnum-dominated lawns with thawing permafrost and 4. inundated, sedge-dominated minerotrophic fens with no permafrost remaining. Permafrost had high extractable inorganic N concentrations, averaging 30 µg N g-1 soil dry weight (dw), whereas extractable P concentrations were low, averaging 1.4 µg P g-1 soil dw. While N concentrations in the permafrost were over four times the concentration in adjacent peatland communities, extractable P concentrations were relatively lower. Sphagnum lawns positioned at the base of palsas, had nine times the extractable P concentrations averaging 12.6 µg P g-1 soil dw compared to the permafrost, suggesting that P availability increases as permafrost thaws. However, in the fen where no permafrost remains, extractable P concentrations were again low, 2.4 µg P g-1 soil dw, despite high total P. These fen communities are also marked by higher iron concentrations, likely resulting in P immobilization by higher concentrations of metals. The addition of inorganic P and the combination of organic N and P in these fen sites strongly enhanced CH4 oxidation rates while organic N did not, indicating the importance of P for these energy intensive transformations. Nutrient amendments did not have a significant effect on CH4 production rates, however, permafrost slurries significantly decreased CH4 production in Sphagnum lawn communities, suggesting an unknown inhibitory effect of permafrost chemistry on CH4 production. The results of our study highlight the effects of permafrost degradation on nutrient release and provide new insight into how nutrients unlocked from permafrost affects greenhouse gases. 

How to cite: Kashi, N. N., Varner, R. K., Thorp, N. R., Knorr, M. A., Wymore, A. S., Ernakovich, J. G., Hobbie, E. A., and Giesler, R.: Nutrients unlocked from permafrost thaw affect microbial methane metabolism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12521, https://doi.org/10.5194/egusphere-egu2020-12521, 2020.

EGU2020-17683 | Displays | CR1.5

Microbial life in collapsing permafrost in NE Greenland

Maria Scheel, Torben R. Christensen, Mats Rundgren, Carsten Suhr Jacobsen, and Athanasios Zervas

In recent years, permafrost-affected soils have been shown to be gradually subject of thawing (IPCC, 2019). Formerly frozen soil organic carbon stocks hence become increasingly susceptible to microbial decomposition and transformation into greenhouse gases (Schuur et al., 2015). An estimated 20% of Arctic permafrost areas are subject of melting of belowground ice and consequent collapse (Olefeldt et al. 2016), but these thermokarst landscapes are often difficult to assess.

In 2018, a thermokarst developed into a thermal erosion gully in close vicinity to the Zackenberg Research Station. As one of the main stations of the Greenland Ecosystem Monitoring (GEM) program, the monitoring of various ecosystem parameters at this site during the past 25 years, including hydrology, soil temperature and active layer depth, enables a spatiotemporally precise description of the thermokarst's physical progression.

In order to characterize the development of a thermokarst soil microbial community and understand its spatial distribution and taxonomic biodiversity, soil cores of 30 cm above and below an ice lens were extracted in August 2018, as well as after a dry and warm summer season in September 2019, until 90 cm depth to also sample still frozen permafrost soils. Soil characterization included loss on ignition, radiocarbon dating and microbial viability assays for both years. Bacterial 16S rDNA V3-V4 and fungal ITS1 gene region amplicons of extracted DNA were sequenced and analyzed. With the microbiome involved in biochemical processes such as nitrogen fixation, methane production and oxidation as well as CO2 respiration, knowledge about abundance, genetic and adaptation potential of bacteria, archaea and microeukaryotes in fast changing permafrost soils affects several ecosystem carbon fluxes significantly.

This work is part of a project, describing both the taxonomic and functional composition of this thermokarst microbiome, including the use of multi-omics to reveal the carbon cycling gene potential and expression in combination with in situ and laboratory incubation gas fluxes of CO2, N2O and CH4. These biological and biogeochemical insights from this event are put into perspective with long-term, maintained data supplied by the GEM. 

How to cite: Scheel, M., Christensen, T. R., Rundgren, M., Suhr Jacobsen, C., and Zervas, A.: Microbial life in collapsing permafrost in NE Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17683, https://doi.org/10.5194/egusphere-egu2020-17683, 2020.

EGU2020-14347 | Displays | CR1.5

Towards the first circumarctic N2O budget – Extrapolating to the landscape scale

Lona van Delden, Maija Marushchak, Carolina Voigt, Guido Grosse, Alexey Faguet, Nikolay Lashchinskiy, Johanna Kerttula, and Christina Biasi

The Arctic is warming at twice the rate of the rest of the globe. While it has been increasingly highlighted that thawing permafrost accelerates soil organic matter decomposition, research on biogeochemical N cycling is still underrepresented. Arctic nitrous oxide (N2O) emissions have long been assumed to have a negligible climatic impact but recently increasing evidence has emerged of N2O hotspots in the Arctic. Even in small amounts, N2O has the potential to contribute to climate change due to it being nearly 300 times more potent at radiative forcing than CO2. Therefore, the ‘NOCA’ project aims to establish the first circumarctic N2O budget. Following intensive N2O flux sampling campaigns at primary sites within Northern Russia and soil N2O concentration measurements from secondary sites across the Arctic, we are now entering the phase of spatial extrapolation. Challenges to overcome are the small-scale heterogeneity of the landscape and incorporating small features that can function as N2O hotspots. Therefore, as a first step in upscaling the N2O fluxes, high resolution imagery is needed. We show here novel high-resolution 3D imagery from an unmanned aerial vehicle (UAV), which will be used to upscale N2O fluxes from plot to landscape scale by linking ground-truth N2O measurements to vegetation maps. This approach will first be applied to the East cliff of Kurungnakh Island in the Lena River Delta of North Siberia and is based on 2019 sampling campaign data. Kurungnakh Island is characterized by ice- and organic-rich Yedoma permafrost that is thawed by fluvial thermo-erosion forming retrogressive thaw slumps in various stages of activity. Overall, 20 sites were sampled along the cliff and inland, covering the significant topographic and vegetative characteristics of the landscape. The data from this scale will provide the basis for extrapolating, by using a stepwise upscaling approach, to the regional and finally circumarctic scale, allowing a first rough estimate of the current climate impact of N2O emissions from permafrost affected soils. Available international circumarctic data from this and past projects will be synthesized with an Arctic N2O database under development for use in future ecosystem and process-based climate model simulations.   

How to cite: van Delden, L., Marushchak, M., Voigt, C., Grosse, G., Faguet, A., Lashchinskiy, N., Kerttula, J., and Biasi, C.: Towards the first circumarctic N2O budget – Extrapolating to the landscape scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14347, https://doi.org/10.5194/egusphere-egu2020-14347, 2020.

CR2.1 – Geophysical and in-situ methods for snow and ice studies

Airborne radar sounding is the primary geophysical method for directly observing conditions beneath ice sheet and glaciers at the catchment to continent scale. From single flow-lines to regional surveys to ice-sheet wide gridded topographic datasets, radar sounding profiles provide information-rich constraints on the englacial and subglacial environment. This can include roughness, lithology, hydrology, thermal state, melt, fabric, and structure for both grounded and floating ice. However, the snap-shot view provided by one-time soundings fails to capture subsurface processes across the time-scales over which they evolve and control ice flow.  Doing so requires advancing multi-temporal radar sounding instruments, platforms, and data analysis. For example, point-measurements by ground-based or stationary sounder can be used produce local time-series observations of englacial and subglacial conditions. However, low-cost, low-power active and/or passive radar-sounder networks can dramatically extend the reach and scope of such measurements. Further, repeat surveys by sled-drawn or airborne sounders can capture seasonal and interannual subsurface variations. However, digitization of archival radar film are extending the temporal baseline for such comparison by decades, making multi-decadal studies of subsurface changes possible. Finally, the development of autonomous rover, drone, and satellite sounding platforms and systems promise to enable pervasive, stable, and frequent monitoring of subglacial conditions. Here, we discuss the advances, challenges, and the path forward to observing subsurface conditions across the full range spatial and temporal scales at which they occur.

How to cite: Schroeder, D.: Observing Evolving Subglacial Conditions with Mutitemporal Radar Sounding , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-179, https://doi.org/10.5194/egusphere-egu2020-179, 2020.

EGU2020-19599 | Displays | CR2.1 | Highlight

Glaciological setting and subglacial conditions at Little Dome C, the future site for Beyond Epica – Oldest Ice Core

Julius Rix, Robert Mulvaney, Carlos Martin, Catherine Ritz, and Massimo Frezzotti

Ice domes in the interior of East Antarctica are ideal candidates in the quest for the longest continuous record of climate in polar ice. They are in areas with low surface precipitation, low horizontal advection and large ice thickness. However, the age of the ice near the bottom of the column is very sensitive to subglacial thermal conditions as they can promote basal melting and the loss of the bottommost and oldest ice. Here we report the main findings from a geophysical survey and a shallow, 460m depth, rapid access drilled borehole. We use a low frequency radar, DELORES, to survey the area and detect subglacial melting; a phase sensitive radar, ApRES, to obtain englacial vertical strain-rates and crystal orientation fabrics in selected sites; and, at the drilling site, borehole temperature and water isotope data in the top 460m. Our main findings are: 1) The subglacial topography is characterized by topographic highs criss-crossed by deep valley troughs with typically 0.5-1km difference in height. There is evidence of subglacial melting in the troughs. However the ice stratigaphy, that we survey in detail with DELORES system with 500m grid, drapes over the rough topography and the topographic highs are presently melt-free. 2) The optical birefringence, observed in ApRES polarimetry, shows two aligned crystal orientation fabrics that are typical for glacial periods. This indicate uniform ice-flow conditions during, at least, the last two glacial-interglacial periods and is consistent with the polarimetry from EPICA Dome C. 3) Using the borehole temperature, englacial strain-rates and temperature records from EPICA Dome C we estimate that the geothermal heatflux in the area is 55 +/- 1 mW/m2. Also we find that, due to the delay between basal and surface temperatures, the basal temperature at Little Dome C is currently the coldest and was 0.5 C warmer 80 kyrs ago. We estimate that any topographic high where the ice thickness is below 2810 +/- 10 m was melt-free during the warmest conditions. This information, together with other evidence, lead to choosing the site for the future Beyond Epica – Oldest Ice Core project.

How to cite: Rix, J., Mulvaney, R., Martin, C., Ritz, C., and Frezzotti, M.: Glaciological setting and subglacial conditions at Little Dome C, the future site for Beyond Epica – Oldest Ice Core, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19599, https://doi.org/10.5194/egusphere-egu2020-19599, 2020.

EGU2020-21606 | Displays | CR2.1

Radio-wave reflectivity from cold glaciers

Olga Yushkova, Taisiya Dymova, and Viktor Popovnin

Radio echo-sounding is a powerful technique for investigating the subsurface of the glaciers. However, physics underlying the formation of the reflected signal is sometimes oversimplified  in the geophysical glacier studies, leading to wrong results. Various remote sensing techniques use different wavelengths (e.g., 13.575 GHz for CryoSat and 20-25/200-600 MHz for ground-penetrating radar), but it is still not clear which particular wavelengths are the best to detect different characteristics of the ice. Possibly, the results gained using different wavelengths may not coincide but rather complement each other due to frequency dependence of the dielectric permittivity and conductivity of snow, ice and especially water.

Here we attempt to construct an electrophysical model of a cold glacier. This mathematical model considers the variability of the depth profile of the complex dielectric permittivity depending on the frequency of the probing radio signal and the surface temperature. A series of calculations of the reflection coefficients of radio waves from the modelled glacier show that at low temperatures for frequencies above 1 MHz the real part of the dielectric constant of the glacier does not change with frequency and surface temperature, but depends on the glacier structure, while the depth profile of the loss tangent is constant throughout the glacier.  As wavelength decreases, the absorption of radio-waves by the glacier decreases and the frequency dependence of the reflection coefficient becomes a periodic function, its period and amplitude depend on the glacier thickness, the dielectric constant of the bedrock and ice on the surface.

The range of radio-waves from 0.1 to 1 MHz is not optimal for sounding cold glaciers: the absorption of radio-waves by ice is large for studying thick layers of the glacier, and the wavelength does not allow studying thin layers. Hence, reflection from the glacier surface prevails upon reflection of the signal. The small absorption of short radio waves by ice leads to the fact that the frequency dependence of the reflection coefficient of short radio-waves is practically the sum of the partial reflections of radio-waves from the surface and internal snow/firn and firn/ice boundaries. Period and amplitude of oscillations of the function  depend on the depth of the internal boundaries and the gradient of dielectric characteristics of ice, snow, firn and bedrock.

Changes in surface temperature, leading to a change in the loss tangent of the upper glacier layers, are manifested in the phase magnitude of the reflection coefficient of radio-waves:it grows with the temperature. Theoretically, the high-frequency signal reflected from the glacier contains information about the structure of the cold glacier and the depth distribution of the dielectric constant, but to restore the electrophysical parameters of the glaciers, it is necessary to use a broadband signal with smooth spectrum and high digitization speed.

The reported study was funded by RFBR, project number 18-05-60080 (“Dangerous nival-glacial and cryogenic processes and their impact on infrastructure in the Arctic”).

How to cite: Yushkova, O., Dymova, T., and Popovnin, V.: Radio-wave reflectivity from cold glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21606, https://doi.org/10.5194/egusphere-egu2020-21606, 2020.

EGU2020-20424 | Displays | CR2.1

3D Structure of NEGIS shear margins from radar stratigraphy

Daniela Jansen, Steven Franke, Tobias Binder, Paul Bons, Dorthe Dahl-Jensen, Olaf Eisen, Veit Helm, Heinrich Miller, Niklas Neckel, John Paden, Daniel Steinhage, and Ilka Weikusat

The North East Greenland Ice Stream (NEGIS) is delineated by well-defined shear margins, which are evident in the gradient of surface velocity field as well as in the surface topography, where they form troughs up to ten meters deep. In the upper part of the ice stream the margins appear not to be linked to bedrock topography. To understand this efficient system of mass transport towards the ocean it is essential to investigate the nature of the shear margins, as here very localized deformation decouples the inner ice stream from the slower flowing surrounding ice sheet. This process is influenced by several factors and feedback mechanisms, including the crystal fabric orientation, strain heating and localization of meltwater. In summary, the shear margins are area-wise a small part of the ice stream itself, but the processes leading to the localization of deformation are of similar importance for ice discharge as the processes enabling fast flow of the main trunk over the bed.

We present results from an airborne radar survey with the AWI Ultra-Wide Band Radar system, covering an area 150 km upstream and 100 km downstream of the deep drilling site on the ice stream (EGRIP). Over the survey area the ice stream accelerates from 12 m/a to 75 m/a. We focus on the signatures of the shear margins in the radar data. In the regions of localized shear, the internal reflections in the radargrams show disturbances in the form of steep undulations, or chevron folds, which are intensified with ongoing shear. As the ice stream has been covered with 36 flow-perpendicular radar sections we are able to show the evolution of these characteristic signatures over the survey area, and thus, as an analog, over time. 3D-representations of the folded stratigraphic layers reveal how new folds are formed when the ice stream widens and how older structures are preserved in the outer part of the main trunk, where they are no longer subject to shear. Furthermore, we link the change of the shape of the internal reflections in the shear zones to a strain rate field calculated from high resolution flow velocities derived by TerraSAR-X data.

How to cite: Jansen, D., Franke, S., Binder, T., Bons, P., Dahl-Jensen, D., Eisen, O., Helm, V., Miller, H., Neckel, N., Paden, J., Steinhage, D., and Weikusat, I.: 3D Structure of NEGIS shear margins from radar stratigraphy , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20424, https://doi.org/10.5194/egusphere-egu2020-20424, 2020.

EGU2020-20484 | Displays | CR2.1

Automated estimation of englacial radar velocity from zero offset data; implications for glacier bed topography retrieval

Richard Delf, Robert G Bingham, Andrew Curtis, Satyan Singh, Benjamin Schwarz, and Antonios Giannopoulos

Ground Penetrating Radar (GPR) is widely used on polythermal and temperate glaciers to sound bed topography and investigate the hydrothermal conditions through detection of englacial radar scattering. Water held within micro- and macro-scale pores and ice grain boundaries in ice at the pressure melting point influences the velocity of radar propagation on the scale of the wavelength, and can result in the occurrence of pronounced diffraction patterns in the data. Methods to investigate the water content distribution quantitatively within temperate ice often require the use of multi-offset common mid-point or common source-point survey techniques, which are logistically challenging and expensive. As a result, bed topography estimation is often undertaken using a constant velocity, and, because lateral variations in the the velocity field are unaccounted for, errors in topography are likely.

Here, we present an automated workflow to estimate an englacial radar velocity field from zero offset data and apply the algorithm to GPR data collected on Von Postbreen, a polythermal glacier in Svalbard, using a 25 MHz zero-offset GPR system. We first extract the diffracted wavefield using local coherent stacking to remove scatter and enhance diffractions. We then use the focusing metric of negative entropy to deduce a local migration velocity field from constant-velocity migration panels and produce a glacier-wide model of local (interval) radar velocity. We show that this velocity field is successful in differentiating between areas of cold and temperate ice and can detect lateral variations in radar velocity close to the glacier bed. The effects of this velocity field in both migration and depth-conversion of the bed reflection are shown to result in consistently lower ice depths across the glacier, indicating that diffraction focusing and velocity estimation are crucial in retrieving correct bed topography in the presence of temperate ice.

How to cite: Delf, R., Bingham, R. G., Curtis, A., Singh, S., Schwarz, B., and Giannopoulos, A.: Automated estimation of englacial radar velocity from zero offset data; implications for glacier bed topography retrieval , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20484, https://doi.org/10.5194/egusphere-egu2020-20484, 2020.

EGU2020-19365 | Displays | CR2.1

Repeated ground-penetrating radar measurements to detect seasonal and annual variations of an englacial conduit network

Gregory Church, Andreas Bauder, Melchior Grab, Cédric Schmelzbach, and Hansruedi Maurer

Surface meltwater is routed through the glacier’s interior by englacial drainage systems into the subglacial drainage system. The subglacial drainage system plays an important control on the glacier sliding velocity. Therefore, studying the evolution of englacial drainage systems throughout the melt season is key to understanding how these englacial drainage systems develop, and how they subsequently feed the subglacial drainage system.

We have conducted 10 repeated ground-penetrating radar using a Sensor & Software pulseEKKO Pro GPR system with 25 MHz antenna between 2012 and 2019 over an englacial conduit network, 90 m below the glacier’s surface, on the Rhonegletscher, Switzerland. These repeated measurements allowed insights into both annual and seasonal changes. We were also able to have direct observations into the englacial conduit network from six boreholes that were drilled in August 2018 using a GeoVISIONTM Dual-Scan borehole camera.

The annual results provided evidence that the englacial drainage network developed between 2012 and 2017. The seasonal evolution of the englacial conduit was studied by inverting the GPR data using an impedance inversion. The impedance inversion delivered reflection coefficients, which provides information on the englacial material properties associated with the englacial conduits. The inversion results provide evidence that during the winter season the englacial network is inactive. During June the englacial network becomes active by transporting surface melt water, and it becomes fully active later in the melt season (August). The reflectivity in summer (June-October) is -0.6, indicating the presence of water within the network. In winter (November-May) the reflectivity is around 0 indicating that the system is neither air or water filled and therefore the system physically closes.

The data processing workflow provided a top and bottom reflection coefficient of the conduit. The travel time between the reflection coefficients can be converted to a thickness when using EM wave velocity of water (from 2018 borehole observations). During the summer months the englacial network is around a quarter wavelength thick (0.3 m), which is approximately the limit of the vertical resolution.

How to cite: Church, G., Bauder, A., Grab, M., Schmelzbach, C., and Maurer, H.: Repeated ground-penetrating radar measurements to detect seasonal and annual variations of an englacial conduit network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19365, https://doi.org/10.5194/egusphere-egu2020-19365, 2020.

EGU2020-22579 | Displays | CR2.1

Monitoring the last Apennine glacier: recent in situ campaigns and modelling of Calderone glacial apparatus

Elena Pettinelli, Massimo Pecci, Frank S. Marzano, Marianna Biscarini, Paolo Boccabella, Federica Bruschi, Tiziano Caira, David Cappelletti, Domenico Cimini, Pinuccio D’Aquila, Thomas Di Fiore, Giulio Esposito, Sebastian E. Lauro, Elisabetta Mattei, Angelo Monaco, Gianluca Palermo, Mattia Pecci, Edoardo Raparelli, Marco Scozzafava, and Paolo Tuccella

The Calderone glacier is at present the most southern glacier in Europe (42° 28' 15’’ N). The little apparatus (about 20.000 m2 in surface area) has been giving an interesting response both to short- and long-term climatic variations which resulted in a considerable reduction in surface area and volume. The glacial apparatus is split into two ice bodies (glacierets) since 2000. The two glacierets are located in a deep northward valley below the top of the Corno Grande (2912 m asl) in the centre of the Gran Sasso d’Italia mountain range (Central Italy). Such glacial apparatus has been subjected to a strong reduction, with a loss of total surface area of about 50% and thickness of about 65%with respect to the hypothetical size (about 105.00 m2 and 55 m at the Little Ice Age).

Since early 90s the Calderone glacier has been subjected to several multidisciplinary field campaigns to monitor and evaluate its role as an environmental indicator in the framework of global warming. Starting from historical series related to more than a century of records, the variability of the different glacier properties has been estimated by using classical geomorphologic methods as well as in situ and remote sensing techniques. In particular, the last field campaigns, in 2015, 2016 and 2019, have been carried out using Ground Penetrating Radar equipped with different antenna frequencies, drone-based survey, snow pit measurements and chemical-physical sampling. The measurement campaigns have been complemented by a regional climate analysis, spanning the last fifty years, and snowpack modelling initialized with microphysical snow data (e.g., snow density, crystal shape and size, hardness).  The snowpack chemical analyses include the main and trace elements, soluble inorganic and organic ions, EC/OC and PAH, with different spatial resolution depending on the analytes. We present here the methodological approach used and some preliminary results.

How to cite: Pettinelli, E., Pecci, M., Marzano, F. S., Biscarini, M., Boccabella, P., Bruschi, F., Caira, T., Cappelletti, D., Cimini, D., D’Aquila, P., Di Fiore, T., Esposito, G., Lauro, S. E., Mattei, E., Monaco, A., Palermo, G., Pecci, M., Raparelli, E., Scozzafava, M., and Tuccella, P.: Monitoring the last Apennine glacier: recent in situ campaigns and modelling of Calderone glacial apparatus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22579, https://doi.org/10.5194/egusphere-egu2020-22579, 2020.

EGU2020-1341 | Displays | CR2.1

Bed-character dependent microseismicity clustering at Rutford Ice Stream, West Antarctica

Sofia-Katerina Kufner, Alex Brisbourne, Andy Smith, Sridhar Anandakrishnan, Tavi Murray, Rebecca Schlegel, Keith Nicholls, Dominic Hodgson, Michael Kendall, and Ian Lee

Microseismicity, induced by the sliding of a glacier over its bed and through bed deformation, can be used to characterize frictional properties of the ice-bed interface. Together with ice column deformation, these characteristics form the key parameters controlling ice stream flow. Here, we use naturally occuring seismicity to monitor temporal and spatial changes in bed properties at Rutford Ice Stream (RIS), West Antarctica, in order to characterize ongoing basal deformation and sliding. RIS is a significant contributor to the outflow of ice from West Antarctica, with speeds of ~1.1 m/day. Past geological and geophysical surveys, including drilling into the bed itself, have revealed pronounced bed topography and a sharp change in bed character along flow direction from presumably soft deformable to stiffer sediments. These complementary data as well as Rutford’s flow characteristics allow us to interpret the seismic data in their geological context.

Our data consist of three months of seismic recordings from a 35-station seismic network located ~40 km upstream the grounding line of RIS, being collected in the framework of the BEAMISH project during the 2018/19 field season. An event catalogue derived using the QuakeMigrate and Nonlinloc software packages reveals an active seismic environment (~40,000 events in three months) with locally clustered microseismicity. Microseismicity occurs near the ice-bed interface and is concentrated in the transition region between presumed-soft and presumed-hard sediments. Within the more compacted sediments further seismicity occurs, predominantly along topographic lows, which form elongated, flow parallel sub-glacial valleys. Within the regions of activity, seismicity tends to cluster in focused spots of particular high activity. Repeated basal seismicity at spatially restricted locations has been observed before and was interpreted as being caused by ‘sticky spots’ within a more ductile deforming matrix. Our results, showing a close alignment of these sticky spots along structural and topographic boundaries, may indicate that such features form major obstacles for basal glacial sliding. In addition to these spatial variations, the average event frequency varies over time. We estimate an ~15 day periodicity to the activity with as many as 1200 events/day during the active times and as few as ~100 events per day during the more-quiescent times. This roughly corresponds to the period of the spring-neap tidal cycle which has been shown to modulate the horizontal flow velocity of RIS. Time dependent variations in the frequency of microseismicity might suggest the glacial bed affected by these modulations.

How to cite: Kufner, S.-K., Brisbourne, A., Smith, A., Anandakrishnan, S., Murray, T., Schlegel, R., Nicholls, K., Hodgson, D., Kendall, M., and Lee, I.: Bed-character dependent microseismicity clustering at Rutford Ice Stream, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1341, https://doi.org/10.5194/egusphere-egu2020-1341, 2020.

EGU2020-11594 | Displays | CR2.1

Imaging the poro-elastic properties of glacier beds using ambient seismic noise monitoring : application to Whillans ice stream, Antarctica

Aurélien Mordret, Gauthier Guerin, Diane Rivet, Brad Lipovsky, and Brent Minchew

Part of the movement that occurs on all glaciers in Antarctica is a continuous and stable movement that unloads the ice into the sea. The Whillans Ice Plain (WIP) is a portion of the Whillans ice stream that measures 8000 km² for an ice thickness of 800 meters. This glacier has a unique characteristic of moving thanks to tidally modulated stick-slip events twice a day. The slip speed varies laterally across the glacier.  We measured surface wave velocity variations computed from ambient seismic noise cross-correlation. The cross-correlations make it possible to monitor temporally and spatially the seismic velocities at the bed of the glacier, associated with changes in poro-elastic parameters and frictional properties of the glacial till. We averaged our observations for the 78 stick-slip events of our dataset and managed to achieve a 5 min temporal resolution along the 45 min long slip events. The results show a decrease in velocity of about 9% of the S-wave velocity in the subglacial sediment layer about 30 minutes after the initiation of the slip. This velocity drop mainly affects the central part of the glacier. A 10% increase in porosity could induce this velocity decrease due to dilatancy. Dilatant strengthening results from this porosity increase, which in turn keeps the glacier in a slow-sliding regime. The high rate of seismic cycles on such a large scale makes the Whillans ice stream a unique laboratory to study transient aseismic slips in glacial context but also in active tectonic faults one. 

How to cite: Mordret, A., Guerin, G., Rivet, D., Lipovsky, B., and Minchew, B.: Imaging the poro-elastic properties of glacier beds using ambient seismic noise monitoring : application to Whillans ice stream, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11594, https://doi.org/10.5194/egusphere-egu2020-11594, 2020.

EGU2020-128 | Displays | CR2.1

Characterising the bed of Rutford Ice Stream, West Antarctica, using reflection seismic profiles

Alex Brisbourne, Andrew Smith, Tavi Murray, Rebecca Schlegel, Keith Nichols, Dominic Hodgson, Sridhar Anandakrishnan, and Sofia Kufner

Ice stream flow is predominantly controlled by sliding over the bed, deformation within the bed and deformation within the ice column. The significance of processes at the bed, now and in the future, remains uncertain due to a lack of knowledge of conditions at the ice stream bed. In the Austral summer of 2018/19, as part of the BEAMISH Project, three holes were drilled to the bed of Rutford Ice Stream to install instruments in the ice column and at the bed, and also sample the bed. Prior to drilling, three seismic profiles were acquired across the bed access sites. These data therefore provide a rare opportunity to compare in situ measurements of ice stream bed conditions with seismic reflection data. The seismic line acquisition was also repeated one year later to investigate any changes at the bed following the drilling and connection to the bed. We will use a combination of imaging, acoustic impedance calculation and wide-angle reflection amplitude variation to characterise the bed conditions using the seismic data.   

How to cite: Brisbourne, A., Smith, A., Murray, T., Schlegel, R., Nichols, K., Hodgson, D., Anandakrishnan, S., and Kufner, S.: Characterising the bed of Rutford Ice Stream, West Antarctica, using reflection seismic profiles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-128, https://doi.org/10.5194/egusphere-egu2020-128, 2020.

EGU2020-8274 | Displays | CR2.1

Constraining subglacial geology using ambient noise Rayleigh wave ellipticity

Glenn Jones, Bernd Kulessa, Ana Ferreira, Martin Schimmel, Andrea Berbellini, and Andrea Morelli

Basal slip is an important mechanism by which glaciers and ice-sheets flow, and is a major source of uncertainty in simulations of ice-mass loss and sea level rise from the Greenland Ice Sheet (GrIS). Sub-ice geology is a dominant control on ice flow velocity with fast flow often coinciding with the presence of deformable subglacial till eroded from underlying sedimentary rocks. The subglacial geology of Greenland has received relatively little attention thus far and its control on ice flow is poorly understood. Seismic studies of the crust beneath the GrIS have been limited due to a lack of seismic stations and the reliance on earthquake event data. However, in the past decade, there has been a rapid increase in the number of both permanent and temporary seismic stations deployed in Greenland as well developments in ambient noise methods, allowing for improved spatial resolution of crustal geology.

 

Ellipticity measurements, the ratio of the horizontal to vertical component of a Rayleigh wave, have been shown to be particularly sensitive to the geological structure directly beneath the station. Ambient noise H/V measurements have been used for decades in geotechnical and civil engineering for site characterisation, making them a well-suited technique to determine the subglacial geology of the GrIS. Using all available broadband stations deployed on Greenland from 2012 to 2018 we extract Rayleigh wave ellipticity measurement from ambient noise data using the degree-of-polarization (DOP) method where meaningful signals are defined as a waveform with an arbitrary polarization which remains stable for a given time window. We invert these ellipticity measurements in the period range of 4 – 9 s to generate Vs profiles of the first 5 km beneath each station. Our inversions indicate that: (1) off-ice stations along the margins of the GrIS produce a good agreement with the litho1.0 model to within error and (2) an additional subglacial layer 1.0 - 2.0km thick with a Vs < 3.0km is necessary to match the data recorded at several of the on-ice stations. We attribute these observations to the widespread presence of sedimentary rocks beneath the GrIS, potentially capable of sustaining extensive subglacial till layers that can support enhanced basal slip.

How to cite: Jones, G., Kulessa, B., Ferreira, A., Schimmel, M., Berbellini, A., and Morelli, A.: Constraining subglacial geology using ambient noise Rayleigh wave ellipticity , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8274, https://doi.org/10.5194/egusphere-egu2020-8274, 2020.

EGU2020-10952 | Displays | CR2.1

Basal Seismicity Forced by Surface-Water Supply on a Stepped-Bed Glacier: Saskatchewan Glacier, Alberta, Canada

Nathan Stevens, Collin Roland, Dougal Hansen, Emily Schwans, and Lucas Zoet

Parameterization of glacier sliding-laws remains a large source of uncertainty in modeling glacier and ice-sheet flow, requiring validation with experimental and observational data. In the case of ice flowing over a till-free, step-shaped bed, theory predicts bed resistance is independent of glacier sliding speed – a “rate neutral” sliding-law (e.g., Iken, 1981). However, experimental simulation of this system resulted in a notable anti-correlation between sliding speeds and bed resistance – a “rate weakening” sliding-law – that may give rise to basal seismicity (Zoet & Iverson, 2016). To investigate this discrepancy, we conducted a seismic field campaign on Saskatchewan Glacier, which is thought to have a stepped bed like those observed in adjacent glacier forefields. The campaign included a dense, 32 seismometer deployment during the middle of the 2019 melt season, complemented by continuous meteorologic, hydrologic, and GPS observations.

Visual and automated characterization of collected seismic data indicate abundant seismicity near the glacier’s bed. Basal seismicity clusters down-flow from an active moulin and a crevassed region likely connected to the bed. Rates of basal seismicity show a strong diurnal signal, consistently occurring 0.5-4 hours after peak surface melting and subglacial discharge, and continuous GPS data indicate temporary ice-flow acceleration during at least two diurnal seismic cycles. Spikes in seismic rate are also observed during most rain events with shorter response-times than diurnal cycles. The diurnal basal seismic cycle was interrupted by two periods of relative quiescence. The first lasted six days, initiating as mean air temperatures and peak daily subglacial discharge rose, and concluding after mean air temperatures and peak discharge declined. The second lasted one day following an abrupt drop in air temperature and was concurrent with reduced subglacial discharge.

We postulate that rapid surface water delivery to the bed strongly influences basal water pressure near delivery points, triggering bursts of seismicity on parts of Saskatchewan Glacier’s bed. Elevated rates of basal seismicity follow peak hydrologic flux through the subglacial drainage system, indicating that stick-slip motion likely occurs as water pressures fall from a transient. Some seismicity is accompanied by temporary acceleration of the glacier, consistent with results from Zoet & Iverson (2016). The six day period of relative quiescence may reflect reorganization of the subglacial hydrologic system into a more efficient drainage network in seismogenic regions, thus damping water pressure transients. Conversely, the one day quiescent period was likely the result of limited surface-water supply. We propose that temporary transitions from stable to stick-slip sliding occurred when basal water pressure exceed a critical threshold on parts of the bed, as modulated by surface-water supply and subglacial drainage efficiency.

Iken, A. (1981). The Effect of the Subglacial Water Pressure on the Sliding of a Glacier in an Idealized Numerical Model. Journal of Glaciology, 27(97).

Zoet, L. K., & Iverson, N. R. (2016). Rate-weakening drag during glacier sliding. Journal of Geophysical Research: Earth Surface, 121, 1328–1350. https://doi.org/10.1002/2016JF003909

How to cite: Stevens, N., Roland, C., Hansen, D., Schwans, E., and Zoet, L.: Basal Seismicity Forced by Surface-Water Supply on a Stepped-Bed Glacier: Saskatchewan Glacier, Alberta, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10952, https://doi.org/10.5194/egusphere-egu2020-10952, 2020.

EGU2020-6385 | Displays | CR2.1

Temporary seismic network on drifting ice in the North Barents Sea

Andrey Jakovlev, Sergey Kovalev, Egor Shimanchuk, Evgeniy Shimanchuk, and Aleksey Nubom

Despite the strong attention to the investigations in the Arctic its advance quite slowly. The harsh climatic conditions and big expenses slow down realization of the fieldwork in high latitudes. Therefore, scientists from over the world looks for new technologies, which could optimize and reduce the costs of the fieldworks that aimed at investigation of the geological structure beneath the Arctic Ocean. From March to May 2019 scientific expedition on the Expedition Vessel “Akademic Tryoshnikov” operated by the Arctic and Antarctic Research Institute that belongs to Rosgidromet were conducted in the framework of the program “TransArctica 2019” first stage. In the framework of the seismological experiments 6 temporary seismic stations at 4 different locations were installed on a drifted ice floe in the North Barents Sea. The first aim of the experiment was to elaborate technology of installation of the seismic stations on the drifting ice floes. The second aim was to check if obtained seismological records could be used for registration of the local and remote earthquakes, which are meant to investigate the lithosphere structure in the Arctic regions, and for investigation of the processes within the ice floe.

The stations were installed in the April 2019 on the ice floe near the EV “Akademik Tryoshnikov” that were “frizzed” in the ice floe and drifted together with them. After analysis of the recoded data the following types of the seismic signal generated by processes in the ice were observed:

  • - background signal from bending-gravitational waves with periods from 1 to 30 sec. Swell waves with periods from 17 to 30 sec were observed permanently during the whole period of network operation;
  • - continuous mechanical vibrations (self-oscillations) with a period of up to 2-3 sec;
  • - stick-slip relaxation self-oscillations with a period from 0.1 s to several minutes;
  • - mechanical movements of ice due to compression or stretching of ice caused by chaotic different scales fluctuations in the drift velocity of ice floes;
  • - process of ice fracturing due to compression or stretching of ice.

Results of monitoring of the ice cover has shown that in the most cases there are no direct correlations of processes within the ice floes and local hydrometeorological condition. During the process of ice cover fracturing an increased value of the ice horizontal movement were observed. Analysis of the seismic signal from ice events has shown that stick-slip events preceded origin of the ice fractures.

As a result of the initial analysis of the seismograms several signals from remote and regional earthquakes were detected. For example, an earthquake that according to the ISC bulletin occur at 08:18:23UTC on April 11, 2019 near the Japan (40.35°N, 143.35°E, 35 km depth, MS = 6.0) were detected. A local earthquake that occur approximately at 05:58UTC on April 10, 2019 at a distance of ~500 km. Due to close location of stations to each other the localization of the earthquake is impossible.

This work is supported by the RSCF project #18-17-00095.

How to cite: Jakovlev, A., Kovalev, S., Shimanchuk, E., Shimanchuk, E., and Nubom, A.: Temporary seismic network on drifting ice in the North Barents Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6385, https://doi.org/10.5194/egusphere-egu2020-6385, 2020.

EGU2020-6916 * | Displays | CR2.1 | Highlight

First Ocean Bottom Seismometer network underneath the ice-covered Arctic Ocean: Operational challenges and chances for monitoring the state of the sea ice cover

Schlindwein Vera, Kirk Henning, Hiller Marc, Scholz John-Robert, and Schmidt-Aursch Mechita

Active and passive seismic monitoring of the cryosphere is mostly done with land seismometers on the surface of ice masses. Seismic monitoring beneath sea ice at the bottom of ice covered oceans has hardly been attempted, because ocean bottom seismometers (OBS) are difficult to recover in perennial sea ice. As a result, for example the tectonic activity of the Arctic mid-ocean ridge system is poorly known. Recently, the ambient seismic noise in long-term seismic records proved a useful tool to monitor the state of the sea ice cover. Since sea ice effectively dampens the formation of wave action, the power in the microseismic noise band, that is mostly generated by ocean wave action, shows seasonal variations which can be explored to study ocean wave climate in relation to the sea ice cover.

From September 2018 - September 2019, we deployed for the first time a network of 4 broadband ocean bottom seismometers at distances of about 10 km at a water depth of roughly 4 km near Gakkel Deep on eastern Gakkel Ridge, Arctic Ocean, from board RV Polarstern. We modified the Lobster-type OBS to include a Posidonia transponder that allowed to accurately track the OBS during descent and ascent and when surfacing underneath an ice floe. We then carefully broke the ice floes until the OBSs appeared in open water and could be recovered.

The network was designed to record local earthquakes along Gakkel Ridge, but it also yields valuable year-round data on the microseismic noise signal at the bottom of the Arctic Ocean in a marginal ice zone.

A first inspection of the data shows a clearly reduced power in the microseismic noise band compared to the Norwegian-Greenland Sea and strongly time dependent noise levels, that may potentially be related to temporary wave action when sea ice retreats during summer. However, the modified OBS structure with a large head buoy fixed to the OBS structure may also be prone to vibrations caused by ocean bottom currents. We will present an initial analysis of the seasonal evolution of the ambient seismic noise that will help to discriminate noise sources and evaluate the potential of such records to monitor the state of the sea ice cover.

How to cite: Vera, S., Henning, K., Marc, H., John-Robert, S., and Mechita, S.-A.: First Ocean Bottom Seismometer network underneath the ice-covered Arctic Ocean: Operational challenges and chances for monitoring the state of the sea ice cover, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6916, https://doi.org/10.5194/egusphere-egu2020-6916, 2020.

EGU2020-7087 | Displays | CR2.1

Comparison of seismic velocities derived from crystal orientation fabrics and ultrasonic measurements on an ice core

Sebastian Hellmann, Johanna Kerch, Melchior Grab, Henning Löwe, Ilka Weikusat, Andreas Bauder, and Hansruedi Maurer

Understanding the internal structure of glacier ice is of high interest for studying ice flow mechanics and glacier dynamics. The micro-scale deformation mechanisms cause a reorientation and alignment of the ice grains resulting in a polycrystalline structure with a strong anisotropy. By studying the crystal orientation fabric (COF), details about past and ongoing ice deformation processes can be derived. Usually, obtaining COF requires a work-intensive ice core analysis, which is typically carried out only at a few ice core samples. When similar information can be obtained from geophysical, for example, seismic experiments, a more detailed and more continuous image about the ice deformation would be available.
For checking the suitability of seismic data for such purposes, we have analysed the COF of several ice core samples extracted from Rhone Glacier, a temperate glacier located in the Central Swiss Alps. The COF analysis yield a polycrystalline elasticity tensor for a given volume of ice, from which we predicted seismic velocities for acoustic waves originating from any azimuth and inclination. The seismic data predicted were then verified with ultrasonic experiments conducted along the ice core in the vicinity of the analysed COF. Additional X-ray tomographic measurements yield further constraints about the microstructure, especially about the air bubble content in the ice affecting the data of the ultrasonic experiments. Predicted and measured velocities generally show a good match. This is a very encouraging result, because it suggests that in-situ measurements of seismic velocities can be employed for studying ice deformation. A possible option is to perform seismic cross-hole measurements within an array of boreholes drilled into the glacier ice.

How to cite: Hellmann, S., Kerch, J., Grab, M., Löwe, H., Weikusat, I., Bauder, A., and Maurer, H.: Comparison of seismic velocities derived from crystal orientation fabrics and ultrasonic measurements on an ice core, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7087, https://doi.org/10.5194/egusphere-egu2020-7087, 2020.

EGU2020-7709 | Displays | CR2.1

Detecting anisotropy using Distributed Acoustic Sensing and fibre-optic seismology in a fast-flowing glacier in Greenland

Adam Booth, Poul Christoffersen, Charlotte Schoonman, Andy Clarke, Bryn Hubbard, Robert Law, Sam Doyle, Tom Chudley, and Athena Chalari

Material anisotropy within a glacier both influences and is influenced by its internal flow regime. Anisotropy can be measured from surface seismic recordings, using either active sources or natural seismic emissions. In the past decade, Distributed Acoustic Sensing (DAS) has emerged as a new, and potentially transformative, seismic acquisition technology, involving determining seismic responses from the deformation of optical fibres. Although DAS has shown great potential within engineering and resources sectors, it has not yet been widely deployed in studies of glaciers and ice masses.

Here, we present results from a glaciological deployment of a DAS system. In July 2019, a Solifos BRUsens fibre optic cable was installed in a 1050 m borehole drilled on Store Glacier in West Greenland. Vertical seismic profiles (VSPs) were recorded using a Silixa iDAS interrogation unit, with seismic energy generated with a 7 kg sledgehammer striking a polyethene (UHMWPE) impact plate. A three-day sequence of zero-offset VSPs (with the source located ~1 m from the borehole top) were recorded to monitor the freezing of the cable, combined with offset-VSPs in along- and cross-flow directions, and radially at 300 m offset.

P-wave energy (frequency ~200 Hz) is detectable through the whole ice thickness, sampled at 1 m depth increments. The zero-offset reflectivity of the glacier bed is low, but reflections are detected from the apparent base of a subglacial sediment layer. S-wave energy is also detectable in the offset VSP records. The zero-offset VSPs show a mean vertical P-wave velocity of 3800 ± 140 m/s for the upper 800 m of the glacier, rising to 4080 ± 140 m/s between 900-950 m. In the deepest 50 m, velocity reduces to 3890 ± 80 m/s. This variation in vertical velocity is consistent with the development of an anisotropic ice fabric in the lowermost 10% of the glacier. The full dataset also contains natural seismic emissions, highlighting the potential of DAS as both an active and passive seismic monitoring tool.

DAS offers transformative potential for understanding the seismic properties of glaciers and ice sheets. The simplicity of the typical VSP geometry makes the interpretation of seismic travel-times less vulnerable to approximations, and thus the derivation of seismic properties more robust, than in conventional surface seismic surveys. As an addition, DAS facilitates VSP recording with unprecedented vertical and temporal resolution. Furthermore, the sensitivity of the optical-fibre to both P- and S-wave particle motion means that a comprehensive suite of acoustic and elastic properties can be inferred.

How to cite: Booth, A., Christoffersen, P., Schoonman, C., Clarke, A., Hubbard, B., Law, R., Doyle, S., Chudley, T., and Chalari, A.: Detecting anisotropy using Distributed Acoustic Sensing and fibre-optic seismology in a fast-flowing glacier in Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7709, https://doi.org/10.5194/egusphere-egu2020-7709, 2020.

EGU2020-15923 | Displays | CR2.1

Application of polarimetric radar to infer ice fabric anisotropy

Mohammadreza Ershadi, Reinhard Drews, Carlos Martín, and Olaf Eisen

Understanding ice flow of ice sheets is not only important to predict their future evolution, but is also required for finding future ice-core sites with an intact stratigraphy and a constrained age-depth relationship of the corresponding climate record. Anisotropic ice flow, induced through the formation of aligned Crystal Orientation Fabric (COF), is in this context important as it may cause ice overturning and folding at larger depths. Here, we use a synthetic radar forward model to explore the feasibility of detecting the crystal orientation fabric orientation and strength using coherent, polarimetric ice-penetrating radar data (ApRES). We compare our results, with ApRES data collected in Antarctica. Some of the sites are located near deep drill ice-core sites (e.g., Dome C), and we validate our approach with ice-core data.

In multilayer models, we distinguish between birefringence (caused by ray propagation through anisotropic COF with unknown strength and orientation) and anisotropic scattering (caused by an unknown depth variability of anisotropic COF). We show analytically that the scattering ratio is determined by the angular dependence of co-polarization extinction nodes. Building on previous work, we infer COF orientation using the depolarization component, and COF strength from the gradient of polarimetric coherence, respectively.

We apply this approach to polarimetric ApRES datasets. We show COF orientation can often reliably be inferred as long as it does not change significantly with depth. Rotation of principal axis with depth, on the other hand, causes a complicated radar response that is not straightforwardly interpreted. At dome positions, where the ice anisotropy develops more gently compared to flank-flow settings, the degree of anisotropy can be estimated with the phase gradient method. This becomes increasingly more difficult for flank-flow settings where phase unwrapping is required. We delineate a number of anisotropic scattering zones which likely correspond to COF patterns changing abruptly. In some cases, boundaries between anisotropic scattering zones coincide with climate transitions within the ice.

We provide our model code in the form of a user-friendly GUI, enabling to quickly explore a wide range of possible COF patterns and their corresponding imprint in the radar data. This is useful both for scientific and educational purposes. Our analysis underlines the potential of coherent, polarimetric radars to infer the COF orientation of ice sheets also away from ice core sites. This will provide important data for the inclusion of ice anisotropy in ice-flow models in the future.

How to cite: Ershadi, M., Drews, R., Martín, C., and Eisen, O.: Application of polarimetric radar to infer ice fabric anisotropy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15923, https://doi.org/10.5194/egusphere-egu2020-15923, 2020.

EGU2020-19541 | Displays | CR2.1

Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow: Observations from South Pole and EPICA Dome C ice cores

Carlos Martin, Howard Conway, Michelle Koutnik, Catherine Ritz, Thomas Bauska, Reinhard Drews, and M. Reza Ershadi

The climatic conditions over ice sheets at the time of snow deposition and compaction imprint distinctive crystallographic properties to the resulting ice. As the snow gets buried, its macroscopic structure evolves due to vertical compression but retains traces of the climatic imprint that generate distinctive mechanical, thermal and optical properties. Because climate alternates between glaciar periods, that are colder and dustier, and interglacial periods, the ice sheets are composed from layers with alternating mechanical properties. Here we compare ice core dust content and crystal orientation fabrics, from the ice core records, with englacial vertical strain-rates, measured with a phase-sensitive radar (ApRES), at South Pole and EPICA Dome C ice cores. Similarly to previous observations, we show that ice deposited during glacial periods develops stronger crystal orientation fabrics. In addition, we show that ice deposited during glacial periods is harder to vertically compress and horizontally extend, up to about 3 times, but softer to shear. These variations in mechanical properties are typically ignored in ice-flow modelling but they could be critical to interpret ice core records. Also, we show that the changes in crystal orientation fabrics due to transitions from interglacial to glacial conditions can be detected by phase-sensitive radar. This information can be used to constrain age-depth in future ice-core locations.

How to cite: Martin, C., Conway, H., Koutnik, M., Ritz, C., Bauska, T., Drews, R., and Ershadi, M. R.: Climatic imprint in the mechanical properties of ice sheets and its effect on ice flow: Observations from South Pole and EPICA Dome C ice cores, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19541, https://doi.org/10.5194/egusphere-egu2020-19541, 2020.

EGU2020-5759 | Displays | CR2.1

Three methods for observing firn densification velocities with phase-sensitive radar

Elizabeth Case and Jonathan Kingslake

Firn densification operates at the boundary between the atmosphere and ice sheets, impacting estimates of ice thickness change, paleoclimate reconstructions, and near-surface hydrology. Direct measurements of firn densification are scarce and firn densification models, which rely mostly on point measurements of density, disagree on the impact of environmental factors like surface temperature and accumulation rate. Phase-sensitive radar systems (pRES) can observe the movement of isochronal layers in firn and ice by tracking the relative two-way travel times (T) of radio waves. In this work, we demonstrate three methods for extracting measurements of densification velocities from pRES data. Method one uses independently measured firn densities to derive compaction velocities. Method two derives vertical velocities in the firn from an inversion that assumes a steady state and exponential density profile. Method three models changes in T using a semi-physical densification model and compares these changes to the pRES observations. We apply each method to radar data from three ice rises in the Weddell Sea Sector of West Antarctica. Results demonstrate how pRES can be used to explore the accumulation dependence of steady-state densification rates. Average accumulation rate is estimated from pRES measurements in areas that are approximately in steady state. Accumulation gradients can be seen across divides (Korff Ice Rise) and densification-rate differences are observed between relatively high (Fletcher Promontory) and low (Skytrain Ice Rise) accumulation environments. With minimal logistic requirements, new pRES systems like autonomous pRES could be inexpensively deployed to monitor firn densification. Furthermore, existing data may contain densification information even in cases when its deployment primarily targeted other processes.

How to cite: Case, E. and Kingslake, J.: Three methods for observing firn densification velocities with phase-sensitive radar, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5759, https://doi.org/10.5194/egusphere-egu2020-5759, 2020.

EGU2020-5307 | Displays | CR2.1

Seismic Full Waveform Inversion (FWI) to characterise the structure of firn

Emma Pearce, Adam Booth, Paul Sava, and Ian Jones

The transformation of snow into ice is a fundamental process in glaciology. The yearly accumulation of fresh snowfall increases the overburden pressure, changing the snow’s properties such that it transitions into firn and pure glacier ice thereafter. Additionally, periods of melt and variations in subsurface and surface conditions can lead to the presence of ice layers and firn aquifers within the firn column. Therefore, firn characteristics provide a tool for evaluating past and present climate conditions relating to the amount of snow accumulation, melt, temperature conditions and the subsequent preservation of the snow.

Due to the importance of relationships between firn and other glaciological processes (e.g., settling, sublimation, recrystallization and other deformation processes) it has not been possible to develop a theoretically-based model which accurately predicts firn properties with depth. Therefore, methods of measuring firn are either intrusive or rely on (potentially unreliable) empirical conversions. Full Waveform Inversion (FWI) may offer a new standard for glaciological seismic modelling, mitigating issues within current seismic modelling techniques and paving the way for the recovery of elastic properties, including density. Constraining firn properties also leads to improved corrections for deeper seismic responses, e.g. glacier bed reflectivity.

 

Using seismic datasets obtained from Norway’s Hardangerjøkulen Ice Cap (60.47°N, 7.49°W) along with varying synthetic firn column scenarios (introducing the presence of ice lenses and firn aquifers), we show how FWI can mitigate the dependence on intrusive techniques and empirical relationships. Furthermore, we compare the robustness of the FWI approaches versus traditional glaciological approaches to velocity model building (Herglotz-Wiechert inversion).

 

How to cite: Pearce, E., Booth, A., Sava, P., and Jones, I.: Seismic Full Waveform Inversion (FWI) to characterise the structure of firn, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5307, https://doi.org/10.5194/egusphere-egu2020-5307, 2020.

Modelling and monitoring seasonal snow is critical for water resource management, flood forecasting and avalanche risk prediction. Snowmelt processes are of particular importance. The behaviour of liquid water in snow has a big influence on melting processes, but is difficult to measure and monitor non-invasively. Recent work has shown the promise of using electrical self potential measurements as a snow hydrology sensor. Self potential magnitudes can be used to infer both liquid water content of snow and bulk meltwater runoff. In autumn 2018, a prototype self potential monitoring array was installed at Col de Porte in the French Alps, alongside full hydrological and meteorological measurements made routinely at the site. Self potential measurements were taken throughout the following winter, with manual snow pit data obtained in spring 2019. A physically-based snow hydrology model was run for the winter, and an electrical model was coupled to the snow model to create a synthetic set of self potential observations. These synthetic observations were compared to the observed self potential magnitudes to evaluate the effectiveness of the snow model, and to investigate the potential for using the self potential array as part of a coupled geophysical monitoring and modelling system.

How to cite: Priestley, A.: In situ geophysical monitoring of liquid water movement in an Alpine snowpack from self potential signals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4851, https://doi.org/10.5194/egusphere-egu2020-4851, 2020.

EGU2020-17824 | Displays | CR2.1

Assessment of operational monitoring of snow water equivalent measurements with low-cost GNSS sensors

Achille Capelli, Franziska Koch, Patrik Henkel, Markus Lamm, Christoph Marty, and Jürg Schweizer

The water stored in the snowpack is a crucial contribution to the hydrological cycle in mountain areas. Estimating the spatial distribution and temporal evolution of snow water equivalent (SWE) in mountain regions is, therefore, a key question in snow hydrology research. For this reason, direct measurements of SWE are still essential, but they are often scarce, not easy to install and maintain, mostly non-continuous or rather expensive. A promising alternative to conventional SWE in-situ measurement methods is a newly developed method based on signals of the freely available Global Navigation Satellite System (GNSS), which can be received with standard low-cost sensors. In general, this measurement technique is based on signal differences between one GNSS antenna buried below the snowpack and one reference antenna above the snow cover. The signal differences reflect the GNSS carrier phase time delay and the GNSS signals strength attenuation within the snowpack, which can be translated into SWE and the snow liquid water content (LWC). So far, this method showed excellent results over several years at the high-alpine test and validation site Weissfluhjoch (Eastern Swiss Alps, 2540 m asl.). Currently, our aim is to assess whether this method is suitable for deriving SWE continuously with reasonable accuracy also at other locations with different characteristics. Therefore, we set up further GNSS sensors at different elevations, where the snow characteristics can vary considerably. At lower elevations the snow cover is normally shallower and is more frequently subject to melt-freeze cycles leading to faster snow aging and different snow densities. Moreover, rapid transition from dry- to wet-snow conditions as well as steep valley sites can be seen as a challenge. In total, we were operating for two season four GNSS stations along a steep elevation gradient (820 m, 1185 m, 1510 m, and 2540 m asl.) within only a few kilometres in the Eastern Swiss Alps. For validation purposes, we monitored SWE and snow height manually and with additional automatic sensors at all locations. We analysed the GNSS SWE derivation accuracy in general and in detail for different meteorological conditions as snowfall, snow settlement, rain on snow and dry or wet snow periods. Eventually, we compared the GNSS results with results from numerical snow cover models.

How to cite: Capelli, A., Koch, F., Henkel, P., Lamm, M., Marty, C., and Schweizer, J.: Assessment of operational monitoring of snow water equivalent measurements with low-cost GNSS sensors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17824, https://doi.org/10.5194/egusphere-egu2020-17824, 2020.

The snow water equivalent (SWE) is a key parameter in hydrology. In the past years, the signals of Global Navigation Satellite System (GNSS) receivers were discovered to be very attractive for SWE monitoring. The set-up of GNSS-based SWE monitoring typically consists of two GNSS receivers, whereas one is placed on the ground to sense the signal attenuation and time delay being caused by the snow pack. A second receiver is placed above the snow and serves as reference receiver. The measurements of both receivers are differenced to eliminate the common effect of errors in the satellite orbits and clocks, satellite phase and code biases and atmospheric errors, while the information on the snow is kept.

In this talk, we discuss the replacement of the reference receiver by a virtual reference station (VRS). The VRS is a virtual GNSS reference station, whose corrections are obtained by interpolation of the corrections from multiple surrounding reference stations to achieve a higher accuracy at the user location. The concept of VRS was first developed by Trimble and is widely used in today's real-time kinematic (RTK) positioning receivers. The concept of VRS is also attractive for snow monitoring, since the GNSS reference receiver could be avoided resulting in a lower power consumption and less costs. Moreover, this could be a big advantage for applications in slopes, which are, e.g., potentially avalanche prone. Within the hardware setup of our GNSS SWE sensors, an internet communication link for the reception of the corrections from the VRS corrections at the SWE monitoring site is already available.

However, there are also two challenges: First, the SWE monitoring stations in Alpine areas are typically at a significantly different altitude than the geodetic reference receivers. The differential tropospheric zenith delay is not negligible for altitudinal differences of more than 100 m. Therefore, the differential tropospheric delay needs to be considered either in the determination of VRS corrections or alternatively in the SWE determination. For altitudinal differences of less than 1000 m, the differential tropospheric zenith delay could be approximated by a model with sufficient accuracy. The residual modelling error is projected to the SWE estimate. Second, the use of a VRS instead of a conventional GNSS reference station requires a stronger data link, since the GNSS raw data (pseudoranges, carrier phases and carrier-to-noise power ratio measurements from all tracked satellites) need to be transmitted besides the final SWE results. However, an LTE link is totally sufficient.

Besides the methodology, we will also focus on specific hardware implementations.

How to cite: Henkel, P., Lamm, M., and Koch, F.: Determination of Snow Water Equivalent with only one Global Navigation Satellite System receiver and a Virtual Reference Station, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20935, https://doi.org/10.5194/egusphere-egu2020-20935, 2020.

EGU2020-10131 | Displays | CR2.1

Prospecting alpine permafrost with Spectral Induced Polarization in different geomorphological landforms

Theresa Maierhofer, Timea Katona, Christin Hilbich, Christian Hauck, and Adrian Flores-Orozco

Permafrost regions are highly sensitive to climate changes, which has significant implications for the hydrological regimes and the mechanical state of the subsurface leading to natural hazards such as rock slope failures. Therefore, a better understanding of the future evolution and dynamics of mountain permafrost is highly relevant and monitoring of the thermal state of permafrost has become an essential task in the European Alps. Geophysical methods have emerged as well-suited to support borehole data and investigate the spatial distribution and temporal changes of temperature and the degradation of permafrost. In particular, electrical resistivity tomography (ERT) has developed into a routine imaging tool for the quantification of ice-rich permafrost, commonly associated with a significant increase in the electrical resistivity. However, in many cases, the interpretation of the subsurface electrical resistivity is ambiguous and additional information would improve the quantification of the ice content within the subsurface. Theoretical and laboratory studies have suggested that ice exhibits a characteristic induced electrical polarization response. Our results from an extensive field programme including many morphologically different mountain permafrost sites now indicate that this IP response may indeed be detected in the field suggesting the potential of the Induced Polarization (IP) method to overcome such ambiguities. We present here Spectral IP (SIP) mapping results conducted over a broad range of frequencies (0.1-225 Hz) at four representative permafrost sites of the Swiss-, Italian- and Austrian Alps. The mapping results have been used to install long-term permafrost monitoring arrays for a better understanding of subsurface variations associated to climate change. All SIP study sites are located at elevations around 2600 - 3000 m and include comprehensive geophysical and temperature data for validation. We focus on the spatial characterization of each site to address different research questions: to (i) reproduce and improve the mapping of the spatial permafrost extent inferred from previous investigations in the Lapires talus slope,Western Swiss Alps, to (ii) improve the geophysical characterization of the Sonnblick monitoring site located in the Austrian Central Alps, to (iii) determine the transition between permafrost and non-permafrost at the Schilthorn site, Bernese Alps, Switzerland, and to (iv) find the best-suited location for a SIP monitoring profile and conduct year-round measurements at the Cime Bianche site, Western Italian Alps. Our various field applications demonstrate the potential of the IP method for characterizing and monitoring permafrost systems in high-mountain environments.

How to cite: Maierhofer, T., Katona, T., Hilbich, C., Hauck, C., and Flores-Orozco, A.: Prospecting alpine permafrost with Spectral Induced Polarization in different geomorphological landforms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10131, https://doi.org/10.5194/egusphere-egu2020-10131, 2020.

EGU2020-20081 | Displays | CR2.1

Improved thermal characterization of alpine permafrost sites by broadband SIP measurements

Jonas K. Limbrock, Maximilian Weigand, and Andreas Kemna

Geoelectrical methods are increasingly used for non-invasive characterization and monitoring of permafrost sites, since the electrical properties of the subsoil are sensitive to the phase change of liquid to frozen water. In this context, electrical subsurface parameters act as proxies for temperature and ice content.  However, it is still challenging to distinguish between air and ice in the pore space of the rock based on the resistivity method alone due to their similarly low electrical conductivity. This ambiguity in the subsurface conduction properties can be reduced by considering the spectral electrical polarization signature of ice using the Spectral Induced Polarization (SIP) method, in which the complex, frequency-dependent impedance is measured. These measurements are hypothesized to allowing for the quantification of ice content (and thus differentiation of ice and air), and for the improved thermal characterization of alpine permafrost sites.

In the present study, vertical SIP sounding measurements have been made at different alpine permafrost sites in a frequency range from 100 mHz to 45 kHz. From borehole temperature measurements, we know the thermal state of these sites during our SIP soundings, i.e., an active layer thickness of about 4 m at the Schilthorn field site. In order to understand and to calibrate ice and temperature relationships, the electrical impedance was likewise measured on water-saturated soil and rock samples from these field sites in a frequency range from 10 mHz to 45 kHz during controlled freeze-thaw cycles (+20°C to -40°C) in the laboratory.

For field and laboratory measurements, the resistance (impedance magnitude) shows a similar temperature dependence, with increasing resistance for decreasing temperatures. For each sample, the impedance phase spectra exhibit the well-known temperature-dependent relaxation behavior of ice at higher frequencies (1 kHz - 45 kHz), with an increasing polarization magnitude for lower temperatures or larger depths of investigation, respectively. At lower frequencies (1 Hz - 1 kHz), a polarization with a low frequency dependence is observed in the unfrozen state of the samples. We interpret this response as membrane polarization, considering that it decreases in magnitude with decreasing temperature (i.e., with ongoing freezing).

Using the independently measured borehole temperature data, a systematic comparison of the SIP laboratory and field measurements indicates the possibility of a thermal characterization of an alpine permafrost site using SIP.

How to cite: Limbrock, J. K., Weigand, M., and Kemna, A.: Improved thermal characterization of alpine permafrost sites by broadband SIP measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20081, https://doi.org/10.5194/egusphere-egu2020-20081, 2020.

EGU2020-5104 | Displays | CR2.1

The use of Frequency Domain Electro-magnetometry for the characterization of permafrost active layers: case studies in the Swiss Alps

Jacopo Boaga, Marcia Phillips, Jeannette Noetzli, Anna haberkorn, Robert Kenner, and Alexander Bast

The characterization of the active layer (AL) in mountain permafrost is an important part of monitoring climate change effects in periglagical environments and may help to determine potential slope instability. Permafrost affects 25% of the Northern Hemisphere and 17% of the entire Earth. It has been studied for decades both in the polar regions and – starting a few decades later – in high mountain environments. Typical point information from permafrost boreholes can be extended to wider areas by geophysical prospecting and provide information that cannot be detected by thermal observations alone.

During Summer 2019 we performed several geophysical surveys at permafrost borehole sites in the Swiss Alps. We focused on electrical resistivity tomography (ERT) and Frequency Domain Electro-magnetic techniques (FDEM) to compare the methods and test the applicability of FDEM for active layer characterization, i.e., its thickness and lateral continuity. ERT provides an electrical image of the subsoil and can discern active layer thickness, changes in ground ice and geological features of the subsoil. From a logistic point of view a contactless method such as FDEM would be preferable : i) it can provide electrical properties of the subsoil with no need of physical electrical contact with the soil; ii) it can cover a wider area of exploration compared to ERT, iii) it is faster and data collection is simpler than with ERT due to lighter instruments and less preparation time needed.

Based on the FDEM surveys at the Swiss permafrost sites we were able to detect the frozen/unfrozen boundary and to achieve results that were in agreement with those obtained from classical ERT and borehole temperature data. The results were promising for future active layer monitoring with the contactless FDEM method.

How to cite: Boaga, J., Phillips, M., Noetzli, J., haberkorn, A., Kenner, R., and Bast, A.: The use of Frequency Domain Electro-magnetometry for the characterization of permafrost active layers: case studies in the Swiss Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5104, https://doi.org/10.5194/egusphere-egu2020-5104, 2020.

EGU2020-10334 | Displays | CR2.1

Joint Acoustic and Electrical Measurements for Unfrozen Water Saturation of Frozen Saline Soil

Chuangxin Lyu, Thomas Ingeman-Nielsen, Seyed Ali Ghoreishian Amiri, Gudmund Reidar Eiksund, and Gustav Grimstad

Abstract. The climate change has aroused great concern on the stability and durability of the infrastructure installed on permafrost, especially for frozen saline clay with a large amount of unfrozen water content at subzero temperature. The joint electrical resistivity and acoustic velocity measurements are conducted for frozen saline sand and onsøy clay with 50% clay content and 20~40 g/L salinity in order to determine the unfrozen water content. A systematic program of tests involves the saline sand with different salinity, natural onsøy clay with the variable of temperature and freezing-thawing cycles and reconstituted onsøy clay with distinctive density and salinity. The data analysis of measurement results in combination with previous joint measurements for frozen soil resolves the effect of temperature, salinity, soil type and freezing-thawing cycles on the acoustic and electrical properties. An increase of temperature, fine content and salinity results in a decrease of both acoustic velocity and electrical resistivity. Electrical resistivity is sensitive to salinity, while acoustic velocity changes substantially near thawing temperature. We also find that both natural and reconstituted clay with similar water content and salinity show quite different acoustic velocity and electrical resistivity, which indicates that ice crystal structures are distinctive between natural and reconstituted samples. Besides, P-wave velocity is much more sensitive to the fabric change or induced cracks than electrical resistance during freezing-thawing cycles.  In the end, acoustic models like the weighted equation (Lee et al., 1996), Zimmerman and King’s model (King et al., 1988) and BGTL (Lee, 2002) are applied to the UWS estimates based on P-wave velocity and electrical models like Archine’s law are adopted based on electrical resistance. Both estimated UWS from different methods is not always consistent. The difference can be up to 20%.

Keywords: Frozen Saline Clay, Acoustic Velocity, Electrical Resistance, Unfrozen Water Saturation

References:

King, M. S., Zimmerman, R. W., & Corwin, R. F. (1988, May). Seismic and Electrical-Properties of Unconsolidated Permafrost. Geophysical Prospecting, 36(4), 349-364. https://doi.org/10.1111/j.1365-2478.1988.tb02168.x

Lee, J. S. (2002). Biot–Gassmann theory for velocities of gas hydrate-bearing sediments.

Lee, M. W., Hutchinson, D. R., Collett, T. S., & Dillon, W. P. (1996). Seismic velocities for hydrate-bearing sediments using weighted equation. Journal of Geophysical Research: Solid Earth, 101(B9), 20347-20358. https://doi.org/10.1029/96jb01886

 

How to cite: Lyu, C., Ingeman-Nielsen, T., Ali Ghoreishian Amiri, S., Reidar Eiksund, G., and Grimstad, G.: Joint Acoustic and Electrical Measurements for Unfrozen Water Saturation of Frozen Saline Soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10334, https://doi.org/10.5194/egusphere-egu2020-10334, 2020.

EGU2020-11808 | Displays | CR2.1

Geophysical characterization of inactive/active rock glaciers in the semi-arid Andes using seismic, geoelectrics and GPR

remi valois, Nicole Schafer, Giulia De Pasquale, Gonzalo Navarro, and Shelley MacDonell

Rock glaciers play an important hydrological role in the semiarid Andes (SA; 27º-35ºS). They cover about three times the area of uncovered glaciers and they are an important contribution to streamflow when water is needed most, especially during dry years and in the late summer months. Their characteristics such as their extension in depth and their ice content is poorly known. Here, we present a case study of one active rock glacier and periglacial inactive geoform in Estero Derecho (~30˚S), in the upper Elqui River catchment, Chile. Three geophysical methods (ground-penetrating radar and electrical resistivity and seismic refraction tomography) were combined to detect the presence of ice and understand the internal structure of the landform. The results suggest that the combination of electrical resistivity and seismic velocity provide relevant information on ice presence and their geometry. Radargrams shows diffraction linked to boulders presence but some information regarding electromagnetic velocity could be extracted. These results strongly suggest that such landforms contain ice, are therefore important to include in future inventories and should be considered when evaluating the hydrological importance of a particular region.

 

How to cite: valois, R., Schafer, N., De Pasquale, G., Navarro, G., and MacDonell, S.: Geophysical characterization of inactive/active rock glaciers in the semi-arid Andes using seismic, geoelectrics and GPR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11808, https://doi.org/10.5194/egusphere-egu2020-11808, 2020.

EGU2020-8136 | Displays | CR2.1

Geophysical imaging of permafrost in the SW Svalbard – the result of two high arctic expeditions to Spitsbergen

Mariusz Majdanski, Artur Marciniak, Bartosz Owoc, Wojciech Dobiński, Tomasz Wawrzyniak, Marzena Osuch, Adam Nawrot, and Michał Glazer

The Arctic regions are the place of the fastest observed climate change. One of the indicators of such evolution are changes occurring in the glaciers and the subsurface in the permafrost. The active layer of the permafrost as the shallowest one is well measured by multiple geophysical techniques and in-situ measurements.

Two high arctic expeditions have been organized to use seismic methods to recognize the shape of the permafrost in two seasons: with the unfrozen ground (October 2017) and frozen ground (April 2018). Two seismic profiles have been designed to visualize the shape of permafrost between the sea coast and the slope of the mountain, and at the front of a retreating glacier. For measurements, a stand-alone seismic stations has been used with accelerated weight drop with in-house modifications and timing system. Seismic profiles were acquired in a time-lapse manner and were supported with GPR and ERT measurements, and continuous temperature monitoring in shallow boreholes.

Joint interpretation of seismic and auxiliary data using Multichannel analysis of surface waves, First arrival travel-time tomography and Reflection imaging show clear seasonal changes affecting the active layer where P-wave velocities are changing from 3500 to 5200 m/s. This confirms the laboratory measurements showing doubling the seismic velocity of water-filled high-porosity rocks when frozen. The same laboratory study shows significant (>10%) increase of velocity in frozen low porosity rocks, that should be easily visible in seismic.

In the reflection seismic processing, the most critical part was a detailed front mute to eliminate refracted arrivals spoiling wide-angle near-surface reflections. Those long offset refractions were however used to estimate near-surface velocities further used in reflection processing. In the reflection seismic image, a horizontal reflection was traced at the depth of 120 m at the sea coast deepening to the depth of 300 m near the mountain.

Additionally, an optimal set of seismic parameters has been established, clearly showing a significantly higher signal to noise ratio in case of frozen ground conditions even with the snow cover. Moreover, logistics in the frozen conditions are much easier and a lack of surface waves recorded in the snow buried geophones makes the seismic processing simpler.

Acknowledgements               

This research was funded by the National Science Centre, Poland (NCN) Grant UMO-2015/21/B/ST10/02509.

How to cite: Majdanski, M., Marciniak, A., Owoc, B., Dobiński, W., Wawrzyniak, T., Osuch, M., Nawrot, A., and Glazer, M.: Geophysical imaging of permafrost in the SW Svalbard – the result of two high arctic expeditions to Spitsbergen , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8136, https://doi.org/10.5194/egusphere-egu2020-8136, 2020.

CR2.2 – Present and palaeo-perspectives on ice-sheet dynamics: data, models and comparisons

EGU2020-19740 | Displays | CR2.2

Antarctic ice dynamics - from deep past to deep future

Ricarda Winkelmann, Torsten Albrecht, Julius Garbe, Jonathan Donges, and Anders Levermann

The Antarctic Ice Sheet has undergone extensive retreat and re-advance in its glacial-interglacial history. With progressing anthropogenic climate change, the associated ice dynamics and feedbacks could further lead to persistent and potentially irreversible ice loss from Antarctic drainage basins in the future.

Process-based models, in combination with paleo and modern records, provide the tools to reconstruct the glacial-interglacial history of the Antarctic Ice Sheet, to improve our understanding of the involved processes and critical thresholds, and to better anticipate possible future pathways.

Here we present simulations of the Antarctic Ice Sheet over the past two glacial cycles using the Parallel Ice Sheet Model PISM. As the conditions in particular at the base of the ice sheet are weakly constrained, and proxy data for the climatic forcing over the last glacial cycles is sparse, we assess the sensitivity of the model response with respect to the choice of boundary conditions. We further conduct an ensemble analysis in order to systematically constrain uncertainties with respect to representative model parameters associated with ice dynamics, climatic forcing, basal sliding and bed deformation.

Based on the insights into the dynamic threshold behavior and estimates of the ice sheet’s contributions to global sea-level changes in the past, we investigate the long-term future stability of the Antarctic Ice Sheet under different levels of global warming. We show that the ice sheet exhibits a multitude of temperature thresholds beyond which ice loss into the ocean becomes irreversible. Each of these thresholds gives rise to hysteresis behavior, meaning that the currently observed ice-sheet configuration cannot be regained even if temperatures were to be reversed to their present-day levels.

How to cite: Winkelmann, R., Albrecht, T., Garbe, J., Donges, J., and Levermann, A.: Antarctic ice dynamics - from deep past to deep future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19740, https://doi.org/10.5194/egusphere-egu2020-19740, 2020.

EGU2020-1296 | Displays | CR2.2

Investigating basal thaw as a potential driver of ice flow acceleration in Antarctica

Eliza Dawson, Dustin Schroeder, Winnie Chu, Elisa Mantelli, and Helene Seroussi

Glacial thermal processes exert a fundamental control on ice flow, governing viscosity and frozen-to-thawed transitions at the ice-bed interface. Across Antarctica, frozen bed regions characterized by numerical models and geophysical observations, can also reduce ice flow by increasing basal traction. Some frozen bed regions can separate or confine fast-flowing glaciers and ice streams. Others separate inland catchments with thawed beds from the grounding zone of marine ice-sheet sectors. If regions with frozen bed experienced thawing, such a transition may lead to ice-sheet acceleration, reconfiguration, or retreat. To investigate the potential impact of such a thermal transition, we use the JPL/UCI Ice Sheet System Model (ISSM) to identify vulnerable regions across Antarctica that are close to the basal melting point. We assess the impact of thawing these regions by quantifying resulting volume changes and surface expressions. This allows us to identify the areas of the ice sheet where the thermal regime at the ice-bed interface has the largest potential impact on ice-sheet stability and sea-level contribution. We also examine the potential basal temperature and thaw-propagation thresholds governing this process. We then compare the ISSM results to a selection of ice-penetrating radar sounding observations to refine our constraints of the configuration, distribution, and extent of these thermally critical areas.

How to cite: Dawson, E., Schroeder, D., Chu, W., Mantelli, E., and Seroussi, H.: Investigating basal thaw as a potential driver of ice flow acceleration in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1296, https://doi.org/10.5194/egusphere-egu2020-1296, 2020.

EGU2020-4188 | Displays | CR2.2

Recent developments in modeling ice sheet deformation

Felicity McCormack, Roland Warner, Adam Treverrow, and Helene Seroussi

Viscous deformation is the main process controlling ice flow in ice shelves and in slow-moving regions of polar ice sheets where ice is frozen to the bed. However, the role of deformation in flow in ice streams and fast-flowing regions is typically poorly represented in ice sheet models due to a major limitation in the current standard flow relation used in most large-scale ice sheet models – the Glen flow relation – which does not capture the steady-state flow of anisotropic ice that prevails in polar ice sheets. Here, we highlight recent advances in modeling deformation in the Ice Sheet System Model using the ESTAR (empirical, scalar, tertiary, anisotropic regime) flow relation – a new description of deformation that takes into account the impact of different types of stresses on the deformation rate. We contrast the influence of the ESTAR and Glen flow relations on the role of deformation in the dynamics of Thwaites Glacier, West Antarctica, using diagnostic simulations. We find key differences in: (1) the slow-flowing interior of the catchment where the unenhanced Glen flow relation simulates unphysical basal sliding; (2) over the floating Thwaites Glacier Tongue where the ESTAR flow relation outperforms the Glen flow relation in accounting for tertiary creep and the spatial differences in deformation rates inherent to ice anisotropy; and (3) in the grounded region within 80km of the grounding line where the ESTAR flow relation locally predicts up to three times more vertical shear deformation than the unenhanced Glen flow relation, from a combination of enhanced vertical shear flow and differences in the distribution of basal shear stresses. More broadly on grounded ice, the membrane stresses are found to play a key role in the patterns in basal shear stresses and the balance between basal shear stresses and gravitational forces simulated by each of the ESTAR and Glen flow relations. Our results have implications for the suitability of ice flow relations used to constrain uncertainty in reconstructions and projections of global sea levels, warranting further investigation into using the ESTAR flow relation in transient simulations of glacier and ice sheet dynamics. We conclude by discussing how geophysical data might be used to provide insight into the relationship between ice flow processes as captured by the ESTAR flow relation and ice fabric anisotropy.

How to cite: McCormack, F., Warner, R., Treverrow, A., and Seroussi, H.: Recent developments in modeling ice sheet deformation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4188, https://doi.org/10.5194/egusphere-egu2020-4188, 2020.

EGU2020-18618 | Displays | CR2.2

Reconstructing surface mass balance from the Greenland ice sheet stratigraphy.

Alexios Theofilopoulos and Andreas Born

Our knowledge of the past surface mass balance on Greenland depends on scarce paleoclimate reconstructions and uncertain climate simulations. However, reconstructions of the internal layering of the ice sheet can provide an independent dataset of accumulation. The thickness of isochronal layers is directly affected by accumulation, but modified over time by the flow of ice. Existing methods can disentangle these two effects only near the ice divide where assumptions of stationarity may be justified. To solve this problem and to obtain a spatially comprehensive reconstruction of accumulation, we use an ice sheet model with an isochronal grid. Thinning rates are calculated prognostically by the model and can be used to define an inverse problem that can be solved iteratively. The only input data is the final layer thickness of the target, e.g., reconstructed radio echo layers from the Greenland ice sheet. To test this method and its limitations, we reconstruct the accumulation histories from the stratigraphies of simulations for which the idealized accumulation time series and spatial distributions are known. These simulations represent a two-dimensional cross section of the Greenland ice sheet. The results are robust to a wide range of realistic variations in accumulation for all but the layers closest to the bedrock where the deformation by the flow is most severe.

How to cite: Theofilopoulos, A. and Born, A.: Reconstructing surface mass balance from the Greenland ice sheet stratigraphy., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18618, https://doi.org/10.5194/egusphere-egu2020-18618, 2020.

EGU2020-19036 | Displays | CR2.2

Reconstruction of LGM ice extents in Europe indicates a cold and dry climate with precipitation patterns similar to present day

Vjeran Višnjević, Frederic Herman, and Günther Prasicek

 

During the pinnacle of the last glacial period 21 kyr ago, the Alps and the Pyrenees were largely covered by ice. Climate was colder and most likely drier, but the magnitudes of temperature and precipitation changes remain poorly constrained. This is in part because climate proxies are not sufficiently accurate, and because there are unknowns on the past position of the Westerly winds and, consequently, the intensity of the moisture flow towards Europe. A new inverse method combined with an ice flow model enables us to infer past climate from mapped ice extents. In the case of the Alps, all of the presented scenarios recover an increase in the position of the ELA across the mountain range from west to east, and a decrease from north to south, pointing to a dominantly zonal circulation with Westerlies bringing moisture from the Atlantic. This is supported by the Pyrenees reconstruction, where the method recovers a clear N-S gradient for all scenarios, indicating that the moisture source from the direction of the Atlantic. While the precipitation pattern was probably not much different from today, mean temperatures were ~9.3 ± 2.97˚C lower in the Alps and ~6.6 ± 1.6˚C lower in the Pyrenees. Our results match pollen-based reconstructions if the climate was 60% dryer than today.

 

How to cite: Višnjević, V., Herman, F., and Prasicek, G.: Reconstruction of LGM ice extents in Europe indicates a cold and dry climate with precipitation patterns similar to present day, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19036, https://doi.org/10.5194/egusphere-egu2020-19036, 2020.

The Cordilleran Ice Sheet (CIS) repeatedly covered western Canada during the Pleistocene and attained a volume and area similar to that of the present-day Greenland Ice Sheet. Deglaciation of the CIS following the Last Glacial Maximum (LGM) directly affected atmosphere and ocean circulation, eustatic sea level, and human migration from Asia to North America. It has recently been shown that the rapid climate oscillations at the end of the Pleistocene had a dramatic effect on the CIS. Data on glacial isostatic adjustment and cosmogenic nuclide exposure ages indicate that abrupt warming at the onset of the Bølling-Allerød caused significant thinning of the ice sheet, resulting in a fifty percent reduction in mass, while the Younger Dryas cooling caused the expansion of alpine glaciers across the mountains of western Canada. However, the mountainous subglacial terrain makes it challenging to reconstruct the regional-scale deglaciation dynamics of the ice sheet, and its configuration during this period of rapid change remains poorly constrained. 

Here we use the glacial landform record to reconstruct the ice sheet configuration for the central sector of the CIS, over the Cassiar and Omineca Mountains in northern British Columbia, during the Late Pleistocene climate reversals. We present the first regional-scale reconstruction of the CIS following the Bølling-Allerød warming, whereby the ice sheet was reduced to a labyrinth of valley glaciers fed by ice dispersal centres located over the Skeena Mountains in the south and Coast Mountains in the west. Additionally, numerous lateral and terminal late glacial moraines delineate the extent of alpine glaciers, ice caps and ice fields that regrew on mountain peaks above the CIS during the Younger Dryas. Cross-cutting relationships indicate that the valley glaciers of the CIS were slower to respond to the Younger Dryas cooling than the mountain glaciers.

How to cite: Dulfer, H. and Margold, M.: Reconstructing the Cordilleran Ice Sheet in northern British Columbia during the Late Pleistocene climate reversals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-480, https://doi.org/10.5194/egusphere-egu2020-480, 2020.

Compared with the intensely studied interval of the last glacial maximum and termination, significantly less attention has been given to the preceding glacial period and Termination 2. This is perhaps understandable as the Greenland ice cores do not stretch this far back in time and the terrestrial record of the ice sheets has in part been lost during the subsequent glacial period. However, there are many questions remaining about how these two glacial intervals differed and whether this was important in driving some of the differences between the last interglacial and our current interglacial. Here I will focus on a new speleothem record from northern Spain which records the meltwater-driven d18O anomaly in the eastern North Atlantic and provides an absolutely dated chronology (U/Th) during the penultimate glacial and Termination 2. The character of which differs dramatically from a record for Termination 1 recovered from speleothems at the same site. This record also shows structure during Termination 2 that has not been seen previously. Here I’ll discuss some possible reasons for the differences between the two glacial terminations and focus on recent ice sheet model experiments that have been run to try and test these hypotheses.

 

How to cite: Gasson, E., Stoll, H., and Cacho, I.: Contrasting style and retreat rates of the northern hemisphere ice sheets during the past two glacial terminations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20521, https://doi.org/10.5194/egusphere-egu2020-20521, 2020.

EGU2020-6021 | Displays | CR2.2

Impacts of initialisation of coupled ice sheet-ocean models forecasting.

Daniel Goldberg, Paul Holland, and Mathieu Morlighem

In recent years, there have been great advances in coupled ice sheet-ocean modelling, to the point where ice-ocean interactions can be represented in global climate models — with potential to greatly improve forecasting of marine ice-sheet loss and sea level rise in the coming century and beyond. However, initialisation of coupled ice sheet-ocean models has not yet been properly examined; and initialisation approaches applied to ocean and coupled atmosphere-ocean models may not be appropriate due to the long time scales inherent in dynamic ice sheets. Moreover, as ocean melt rates and ice-shelf geometry strongly influence each other, nonphysical transients in incorrectly initialised coupled ice-ocean models may persist for longer than in ice-sheet models alone.

In this work, two approaches to coupled initialisation are considered using a synchronously coupled ice-ocean model. The two approaches are based on two commonly used approaches to ice sheet model initialisation: “snapshot” calibration, where ice-sheet basal and internal parameters are configured to optimise fit with observed surface velocity; and “transient” calibration, where these parameters are configured to jointly optimise fit with velocity and geometry change; however, the transient calibration makes use of the ocean component to ensure the ice model is not subject to “initialisation shock” from ocean melting. The approaches are applied to Smith Glacier, a small but fast-thinning glacier in West Antarctica, and the model is forced under ocean warming scenarios in multidecadal runs. Initially there is much faster retreat seen in the Snapshot-calibrated simulation, but this difference decays over several decades, and ultimately the Transiently-calibrated model sees more retreat.

The experiments further suggest that Smith Glacier is not likely to exhibit Marine Ice Sheet instability in the next century. But the methods discrepancy has strong implications for glaciers which are susceptible to this instability.

How to cite: Goldberg, D., Holland, P., and Morlighem, M.: Impacts of initialisation of coupled ice sheet-ocean models forecasting., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6021, https://doi.org/10.5194/egusphere-egu2020-6021, 2020.

EGU2020-17640 | Displays | CR2.2

Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions

Michele Petrini, Colleoni Florence, Kirchner Nina, Hughes Anna L. C., Camerlenghi Angelo, Rebesco Michele, Lucchi Renata G., Forte Emanuele, Colucci Renato R., Noormets Riko, and Mangerud Jan

An interconnected complex of ice sheets, collectively referred to as the Eurasian ice sheets, covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP), connecting to the Scandinavian Ice Sheet to the south. Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. Investigating key processes driving the last deglaciation of the Barents Sea Ice Sheet represents an important tool to interpret recent observations in Antarctica over the multi-millennial temporal scale of glaciological changes. We present results from a statistical ensemble of ice sheet model simulations of the last deglaciation of the Barents Sea Ice Sheet, all forced with transient atmospheric and oceanic conditions derived from AOGCM simulations. The ensemble of transient simulations is evaluated against the data-based DATED-1 reconstruction. We find that the simulated deglaciation of the Barents Sea Ice Sheet is primarily driven by the oceanic forcing, with sea level rise and surface melting amplifying the ice sheet sensitivity to ocean warming over relatively short intervals. Despite a large model/data mismatch at the western and eastern ice sheet margins, the simulated and DATED-1 deglaciation scenarios agree well on the timing of the deglaciation of the central and northern Barents Sea. The primary role played by ocean forcing in our simulations suggests that the long-term stability of the West Antarctic Ice Sheet could be at stake if the current trend in ocean warming will continue.

How to cite: Petrini, M., Florence, C., Nina, K., Anna L. C., H., Angelo, C., Michele, R., Renata G., L., Emanuele, F., Renato R., C., Riko, N., and Jan, M.: Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17640, https://doi.org/10.5194/egusphere-egu2020-17640, 2020.

EGU2020-10118 | Displays | CR2.2

Quaternary evolution of the northern North Sea

Christine Batchelor, Dag Ottesen, Benjamin Bellwald, Sverre Planke, Helge Løseth, Sverre Henriksen, Ståle Johansen, and Julian Dowdeswell

The North Sea has arguably the most extensive geophysical data coverage of any glacier-influenced sedimentary regime on Earth, enabling detailed investigation of the thick (up to 1 km) sequence of Quaternary sediments that is preserved within the North Sea Basin. At the start of the Quaternary, the bathymetry of the northern North Sea was dominated by a deep depression that provided accommodation for sediment input from the Norwegian mainland and the East Shetland Platform. Here we use an extensive database of 2D and 3D seismic data to investigate the geological development of the northern North Sea through the Quaternary.

Three main sedimentary processes were dominant within the northern North Sea during the early Quaternary: 1) the delivery and associated basinward transfer of glacier-derived sediments from an ice mass centred over mainland Norway; 2) the delivery of fluvio-deltaic sediments from the East Shetland Platform; and 3) contourite deposition and the reworking of sediments by contour currents. The infilling of the North Sea Basin during the early Quaternary increased the width and reduced the water depth of the continental shelf, facilitating the initiation of the Norwegian Channel Ice Stream.

How to cite: Batchelor, C., Ottesen, D., Bellwald, B., Planke, S., Løseth, H., Henriksen, S., Johansen, S., and Dowdeswell, J.: Quaternary evolution of the northern North Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10118, https://doi.org/10.5194/egusphere-egu2020-10118, 2020.

EGU2020-12243 | Displays | CR2.2

Camp Century ice core basal sediments record the absence of the Greenland Ice Sheet within the last million years

Andrew Christ, Paul Bierman, Dorthe Dahl-Jensen, Jørgen Steffensen, Dorothy Peteet, Elizabeth Thomas, Owen Cowling, Eric Steig, Lee Corbett, Joerg Schaefer, Alan Hidy, Marc Caffee, Tammy Rittenour, Jean-Louis Tison, Pierre-Henri Blard, Marie Protin, and John Southon

The Greenland Ice Sheet (GrIS) is melting in response to a rapidly warming climate.  It is imperative to understand GrIS sensitivity to past climate, especially during periods when the ice sheet was smaller than present or possibly absent. The Camp Century ice core from NW Greenland, collected in 1966 and the first ice core to be drilled to the bed of the GrIS, revolutionized our understanding of global paleoclimate since 125 ka. However, basal sediment from the ice core was not fully explored and then sat in storage for decades – until it was re-discovered two years ago. We are now investigating these unique samples from the sub-glacial environment using modern analyses. 

Here, we present initial results from two samples, the upper and lower portions of >4 m of basal sediment. We applied an array of geochemical analyses to characterize paleoenvironment (lipid biomarkers, δ13C, δ15N), to infer past climatic conditions (δ18O, δD) from frozen pore water, and to determine the exposure and burial history of the sediments below the ice sheet (optically stimulated luminescence [OSL], cosmogenic 10Be, 26Al, and 21Ne). 

The sub-glacial sediment consists of poorly sorted, reddish-brown, quartz-rich diamict, with paleo-permafrost features in some layers. This material contains woody macrofossils, fungal sclerotia (Cenococcum geophilum), and mosses (Tomenthypnum nitens, Polytrichum juniperinum) that yield a 14C age >55 ka. Woody tissue from the upper and lower samples yield stable δ13C ratios of -26.7±0.1‰ and -29.6±0.1‰ and δ15N ratios of 2.4±0.8‰ and -2.3±0.8‰. Leaf wax (n-alkanoic acid) distributions are similar to modern Arctic shrubs. Frozen pore water yielded δ18O ratios of -23.06±0.08‰ and -21.49±0.08‰, enriched relative to all overlying ice (<-27‰). Deuterium-excess values are 4.3±0.8 ‰ and 13.4±0.4 ‰, respectively.  These stable isotope measurements of pore water suggest snowfall precipitation at temperatures similar to today if the site were ice-free. OSL measurements from the lower sediment suggest a minimum depositional age >600 ka. In situ 10Be concentrations in quartz decrease with depth from 7.7±0.1 x104 atoms/g (500-850 µm) and  6.6±0.2 x104 (250-500 µm) in the upper sediment to 1.6±0.1 x104 atoms/g (500-850 µm) and 1.8±0.1 x104 (250-500 µm) in the lower sediment. The 26Al/10Be ratio also decreases with depth. In the upper sediment, 26Al/10Be ratios range between 4.2 and 4.9 indicating > 900 ka of burial. In the lower sediment, 26Al/10Be ratios range from 1.4 to 2.0 indicating >2 Ma of burial. Measured 21Ne/10Be ratios in quartz exceed 1000, which could indicate long-term burial and/or the presence of nucleogenic 21Ne.

These results demonstrate that Camp Century basal sediment was exposed under ice-free conditions that supported vegetation similar to today. Cosmogenic data indicate the deeper sediment has been buried for most of the Pleistocene and the OSL date rules out surface exposure of the deeper material at MIS 11. Cosmogenic analysis indicates that the upper sample experienced less burial or more recent re-exposure. These data are consistent with a growing body of evidence indicating a dynamic Pleistocene GrIS, even under a pre-industrial climate system in which atmospheric CO2 concentrations did not exceed ~300 ppm.

How to cite: Christ, A., Bierman, P., Dahl-Jensen, D., Steffensen, J., Peteet, D., Thomas, E., Cowling, O., Steig, E., Corbett, L., Schaefer, J., Hidy, A., Caffee, M., Rittenour, T., Tison, J.-L., Blard, P.-H., Protin, M., and Southon, J.: Camp Century ice core basal sediments record the absence of the Greenland Ice Sheet within the last million years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12243, https://doi.org/10.5194/egusphere-egu2020-12243, 2020.

EGU2020-8691 | Displays | CR2.2

Glaciotectonics and tunnel valleys in the southeastern North Sea imaged by high-resolution multi-channel seismics

Arne Lohrberg, Sebastian Krastel, Daniel Unverricht, and Klaus Schwarzer

Glaciotectonic disturbance of sediments and tunnel valleys are often found near the margin of former ice sheets. Hence, these landforms can be used to reconstruct the dynamics of former ice sheet margins. The direction of thrusts usually points perpendicular to the ice front. Considering heterogeneity due to local ice advances, this relation can be used to infer the regional forward direction of large ice lobes. Here, we present a dense grid of high-resolution 2D multi-channel reflection seismic data from the German sector of the southeastern North Sea imaging a buried glaciotectonic complex and tunnel valleys in unprecedented detail.

We have identified individual thrust sheets in an area of approx. 650 km² (combined with recent results of Winsemann et al. (2020)). All thrust sheets are buried and partly eroded at their top. Two major phases of thrusting with two corresponding detachment surfaces have been identified in the subsurface, of which the younger phase led to the deformation of sediments several kilometers further into the foreland. The thickness of individual thrust sheets differs between 180 and 240 m. Some thrust sheets have been cut by the subsequent formation of tunnel valleys with an overall incision direction ranging from east-west to northeast-southwest. The glaciotectonic complex is limited to its southeast by an updipping reflector, which represents the margin of a source depression.

The restauration of cross-sections shows that the thrust sheets transported sediments over more than a kilometer towards the northwest to west, which relates the formation of the thrust sheets and the source depression. The landforms are very similar to a hill-hole pair that led to the foreland thrust sheets, probably as a result of combined bulldozing and gravity spreading in the foreland of the ice margin. Their occurrence and the adjacent tunnel valleys leads us to assume that we identified the marginal position of an Elsterian ice lobe in the southeastern North Sea.

Reference:
Winsemann, J., Koopmann, H., Tanner, D.C., Lutz, R., Lang, J., Brandes, C., Gaedicke, C., 2020. Seismic interpretation and structural restoration of the Heligoland glaciotectonic thrust-fault complex: Implications for multiple deformation during (pre-)Elsterian to Warthian ice advances into the southern North Sea Basin. Quat. Sci. Rev. 227, 1–15. https://doi.org/10.1016/j.quascirev.2019.106068

How to cite: Lohrberg, A., Krastel, S., Unverricht, D., and Schwarzer, K.: Glaciotectonics and tunnel valleys in the southeastern North Sea imaged by high-resolution multi-channel seismics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8691, https://doi.org/10.5194/egusphere-egu2020-8691, 2020.

EGU2020-334 | Displays | CR2.2

Deglaciation of the Kola Peninsula, Arctic Russia, during the Last Glacial-Interglacial Transition

Benjamin Boyes, Lorna Linch, and Danni Pearce

The glacial history of the Kola Peninsula, northwest Arctic Russia, during the Last Glacial-Interglacial Transition (LGIT; c. 18-10 ka) is poorly understood, with some researchers suggesting that the region was glaciated by the Fennoscandian Ice Sheet (FIS; e.g. Hughes et al., 2016), and others suggesting that it was glaciated by an independent Ponoy Ice Cap (e.g. Astakhov et al., 2016). Furthermore, it is unclear if and where there was a periodic ice standstill during the Younger Dryas (c. 12.9-11.7 ka) cold stadial. This is the largest sector of Fennoscandia where glaciation is poorly constrained, which stems from low resolution geomorphological mapping, a lack of sedimentary analyses, and limited dating of glacial landforms and deposits on the Kola Peninsula.

Initial interpretations of geomorphological mapping and sedimentological analyses are presented. High resolution geomorphological mapping has, so far, demonstrated that the Kola Peninsula was glaciated by the FIS, which flowed from the Scandinavian mountains in the west and across the shield terrain of the Kola Peninsula, and not an independent Ponoy Ice Cap, as indicated by the west-east orientation of glacial lineations (e.g. drumlins, crag and tails, mega-scale glacial lineations), moraines, and meltwater channels. Up to four ice streams located in the western Kola Peninsula and the White Sea demonstrated in the glacial lineation record have also been identified. Furthermore, the Younger Dryas margin is proposed to be aligned north-south across the Kola Peninsula, flowing around the Khibiny Mountains, and forming an ice lobe in the White Sea, which is demonstrated by the moraine and meltwater landform assemblage. Moraines and lateral meltwater channels also suggest the Monche-tundra Mountains were exposed as nunataks, and that there were independent cirque and valley glaciers in the Lovozero and Khibiny Mountains at the periphery of the FIS during the Younger Dryas. In addition, glaciotectonised sediments identified in sedimentary analyses indicates the FIS underwent sustained readvances during retreat. This research will provide crucial empirical data for validating numerical model simulations of the FIS, which in turn will further our understanding of (de)glacial dynamics in other Arctic, Antarctic, and Alpine regions.

 

Astakhov, V., Shkatova, V., Zastrozhnov, A. and Chuyko, M. (2016). Glaciomorphological map of the Russian Federation. Quaternary International, 420, pp.4-14.

Hughes, A.L., Gyllencreutz, R., Lohne, Ø.S., Mangerud, J. and Svendsen, J.I. (2016). The last Eurasian ice sheets - a chronological database and time-slice reconstruction, DATED-1. Boreas, 45(1), pp.1-45.

How to cite: Boyes, B., Linch, L., and Pearce, D.: Deglaciation of the Kola Peninsula, Arctic Russia, during the Last Glacial-Interglacial Transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-334, https://doi.org/10.5194/egusphere-egu2020-334, 2020.

EGU2020-1832 | Displays | CR2.2

The evolution of the Patagonian Ice Sheet from 35 ka to the Present Day (PATICE)

Bethan Davies and the PATICE Team

We present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronostratigraphic data. PATICE includes 58,823 landforms and 1,669 ages, and extends from 38°S to 55°S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka (synchronous with the “Little Ice Age”) and 2011 AD. At 35 ka, the PIS covered of 492.6 x103 km2, had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent at 33 – 28 ka from 38°S to 48°S, and earlier, around 47 ka from 48°S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation at 21 – 18 ka, followed by rapid deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at 14 – 13 ka, 11 ka, 5 – 6 ka, 1 – 2 ka, and 0.2 ka. We suggest that 20th century glacial recession is occurring faster than at any time documented during the Holocene. 

How to cite: Davies, B. and the PATICE Team: The evolution of the Patagonian Ice Sheet from 35 ka to the Present Day (PATICE), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1832, https://doi.org/10.5194/egusphere-egu2020-1832, 2020.

EGU2020-118 | Displays | CR2.2

New insights into North Sea tunnel valley infill and genesis from high-resolution 3D seismic data

James Kirkham, Kelly Hogan, Robert Larter, Ed Self, Ken Games, Mads Huuse, Margaret Stewart, Dag Ottesen, Neil Arnold, and Julian Dowdeswell

Tunnel valleys are large (kilometres wide, hundreds of metres deep) channels incised into bedrock and soft sediments by the action of pressurised subglacial meltwater. Discovered over a century ago, they are common across large swathes of North-West Europe and North America. However, many aspects of tunnel valley formation, and the processes by which they are infilled, remain poorly understood. Here, we use new high-resolution 3D seismic reflection data, collected by the geohazard assessment industry, to examine the infill lithology and architecture of buried tunnel valleys located in the central North Sea. The spatial resolution of our seismic data (3.125-6.25 m bin size) represents an order of magnitude improvement in the data resolution that has previously been used to study tunnel valleys in this region, allowing us to examine their infill in unprecedented detail. Inside the tunnel valleys, we identify a suite of buried subglacial landforms, some of which have rarely been reported inside tunnel valleys before. These landforms include a 14-km-long system of segmented eskers, crevasse-squeeze ridges, subsidiary meltwater channels and retreat moraines. Their presence suggests that, in some cases, tunnel valleys in the North Sea were reoccupied by ice following their initial formation, casting doubt on hypotheses which invoke catastrophic releases of water to explain tunnel valley creation.

How to cite: Kirkham, J., Hogan, K., Larter, R., Self, E., Games, K., Huuse, M., Stewart, M., Ottesen, D., Arnold, N., and Dowdeswell, J.: New insights into North Sea tunnel valley infill and genesis from high-resolution 3D seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-118, https://doi.org/10.5194/egusphere-egu2020-118, 2020.

EGU2020-18701 | Displays | CR2.2

Extensive, Gas-charged Quaternary Sand Accumulations of the Northern North Sea and North Sea Fan

Benjamin Bellwald, Sverre Planke, Sunil Vadakkepuliyambatta, Stefan Buenz, Christine Batchelor, Ben Manton, Dmitry Zastrozhnov, Reidun Myklebust, and Bent Kjølhamar

Sediments deposited by marine-based ice sheets are dominantly fine-grained glacial muds, which are commonly known for their sealing properties for migrating fluids. However, the Peon and Aviat hydrocarbon discoveries in the North Sea show that coarse-grained glacial sands can occur over large areas in formerly glaciated continental shelves. In this study, we use conventional and high-resolution 2D and 3D seismic data combined with well information to present new models for large-scale fluid accumulations within the shallow subsurface of the Norwegian Continental Shelf. The data include 48,000 km2 of high-quality 3D seismic data and 150 km2 of high-resolution P-Cable 3D seismic data, with a vertical resolution of 2 m and a horizontal resolution of 6 to 10 m in these data sets. We conducted horizon picking, gridding and attribute extractions as well as seismic geomorphological interpretation, and integrated the results obtained from the seismic interpretation with existing well data.

The thicknesses of the Quaternary deposits vary from hundreds of meters of subglacial till in the Northern North Sea to several kilometers of glacigenic sediments in the North Sea Fan. Gas-charged, sandy accumulations are characterized by phase-reserved reflections with anomalously high amplitudes in the seismic data as well as density and velocity decreases in the well data. Extensive (>10 km2) Quaternary sand accumulations within this package include (i) glacial sands in an ice-marginal outwash fan, sealed by stiff glacial tills deposited by repeated glaciations (the Peon discovery in the Northern North Sea), (ii) sandy channel-levee systems sealed by fine-grained mud within sequences of glacigenic debris flows, formed during shelf-edge glaciations, (iii) fine-grained glacimarine sands of contouritic origin sealed by gas hydrates, and (iv) remobilized oozes above large evacuation craters and sealed by megaslides and glacial muds. The development of the Fennoscandian Ice Sheet resulted in a rich variety of depositional environments with frequently changing types and patterns of glacial sedimentation. Extensive new 3D seismic data sets are crucial to correctly interpret glacial processes and to analyze the grain sizes of the related deposits. Furthermore, these data sets allow the identification of localized extensive fluid accumulations within the Quaternary succession and distinguish stratigraphic levels favorable for fluid accumulations from layers acting as fluid barriers.

How to cite: Bellwald, B., Planke, S., Vadakkepuliyambatta, S., Buenz, S., Batchelor, C., Manton, B., Zastrozhnov, D., Myklebust, R., and Kjølhamar, B.: Extensive, Gas-charged Quaternary Sand Accumulations of the Northern North Sea and North Sea Fan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18701, https://doi.org/10.5194/egusphere-egu2020-18701, 2020.

EGU2020-5410 | Displays | CR2.2

The recession of the Laurentide Ice Sheet in southeast Northwest Territories during the Pleistocene-Holocene transition

Samuel E. Kelley, Brent Ward, Jason Briner, Martin Ross, Philippe Normandeau, and Barrett Elliott

The Laurentide Ice Sheet (LIS) during the Pleistocene-Holocene transition provides a useful natural laboratory for examining the behavior of a mid- to high-latitude ice sheet during a period of climatically driven ice sheet thinning and retreat. While the timing and pattern of Pleistocene recession of the LIS are well-constrained along the southern and eastern margins, there is limited chronology constraining the ice margin retreat along the northwestern margin. Here we present new cosmogenic 10Be exposure ages retreat of the western margin of the LIS during the Pleistocene-Holocene transition. Sampling was performed along three transects located between the northern shore of Great Slave Lake and Lac de Gras. Each of the transects is oriented parallel to the inferred ice retreat direction in an attempt to capture a regional rate of retreat. Our new 10Be cosmogenic exposure ages from the southeastern Northwest Territories demonstrate that regional deglaciation occurred around 11,000 years ago. The population of ages broadly overlaps, indicating that either the retreat occurred within the resolution of our chronology or that the ice sheet experienced widespread stagnation and rapid down-wasting. These ages, not corrected for changes in atmospheric depth due to isostatic rebound, are older than minimum limiting radiocarbon constraints by ~1000 years, indicating that existing LIS reconstructions may underestimate the timing and pace of ice margin recession for this sector. Constraining the timing of the recession of the northwest sector of the LIS has the potential to inform our understanding about the damming of large proglacial lakes, such as Glacial Lake McConnell. The ages from our southern transect, collected from elevated bedrock hills, indicate LIS retreat from through the McConnell basin occurred after 12,000 years ago, and thus constitute maximum limiting constraints on the expansion of Glacial Lake McConnell southeastward into the present-day Great Slave Lake basin. Our chronology, combined with other emerging cosmogenic exposure ages constraining LIS deglaciation indicates retreat of the ice margin over 100s of kilometres during the Pleistocene-Holocene transition, exhibiting no evidence of a significant readvance during the Younger Dryas stadial.

How to cite: Kelley, S. E., Ward, B., Briner, J., Ross, M., Normandeau, P., and Elliott, B.: The recession of the Laurentide Ice Sheet in southeast Northwest Territories during the Pleistocene-Holocene transition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5410, https://doi.org/10.5194/egusphere-egu2020-5410, 2020.

EGU2020-3902 | Displays | CR2.2

Offshore stratigraphic and geomorphological record of northeastern Ireland

Mark Coughlan, Andy Wheeler, Mike Long, Ronan O'Toole, and Matthew Service

The onshore exposures on the northeast coast of the island of Ireland have been well studied in relation to regional glacial advances of the British and Irish Ice Sheet (BIIS) and changes in relative sea level change. These includes sites around Dundalk Bay, Carlingford Lough and Kilkeel in particular. During deglaciation of the BIIS, two important readvance phases are recorded locally; the Clogher Head and Killard Point Stadials. However, the offshore extent and record of these events is still poorly constrained. Understanding the nature and pattern of deglaciation of the offshore sectors of the BIIS is important to any attempt to reconstruct its history after the Last Glacial Maximum.

This study presents a new seismo-stratigraphic analysis of submarine Quaternary deposits nearshore, off the northeast coast of the island of Ireland. This includes multibeam echosounder (MBES), sparker seismic and core data from the areas of offshore Dundalk Bay, Carlingford Lough, Kilkeel and Dundrum Bay. Preliminary analysis of the data reveals a series of geomorphic features in each area including moraines, eskers, drumlinised landscapes, exposed till surfaces and infilled channels. Sediment cores will be used to further groundtruth these features and provide insights into their formation processes and timing. Initial inspection of these cores suggest two diamicton facies, assumed to be subglacial till, in the area of Kilkeel. This presentation will include results to date from this study with the aim of elucidating the glaciation and deglaciation history of geomorphologically complex area.

How to cite: Coughlan, M., Wheeler, A., Long, M., O'Toole, R., and Service, M.: Offshore stratigraphic and geomorphological record of northeastern Ireland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3902, https://doi.org/10.5194/egusphere-egu2020-3902, 2020.

 

Remote sensing has long been used as a powerful tool for the observation in cryospheric sciences. With the advances brought by the ESA Copernicus program, Earth observation goes a step further in its ability to get acquisitions at very high temporal rate. This is even amplified in polar regions due to heliosynchronism of satellites’ orbits. Earth observation shifts from sporadic observations to Earth monitoring.

Observations are a critical aspect for the assessment of geophysical models. The ability of a model to replicate observations is crucial as a benchmark. It also allows to refine our comprehension of Earth systems, such as in cryospheric sciences.

In this work, we are using the regional climate model MAR to compute the surface melt on a domain focusing on the Roi Baudouin Ice Shelf, Queen Maud Land, East Antarctica. From the results, we extract the number of days with surface melt in a region. In parallel, we employ remote sensing to obtain comparison data. Synthetic aperture radar appears as a solution of choice thanks to its day-and-night (critical in polar regions) and atmospheric-free capabilities. Radar backscattering anomalies between different dates are witnesses of substantial increase of soil moisture. Using Sentinel-1 in its wide-swath modes (namely Interferometric Wide Swath and Extra Wide Swath modes) and multiple satellite paths, near-daily acquisitions can be obtained. By comparing the two independent results, we better constraint model’s outputs while also better interpret SAR acquisitions. 

How to cite: Glaude, Q. and Kittel, C.: Comparison Between Surface Melt Days Estimation from a Regional Climate Model and Near-Daily Synthetic Aperture Radar Backscattering, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5561, https://doi.org/10.5194/egusphere-egu2020-5561, 2020.

EGU2020-6995 | Displays | CR2.2

Disintegration of the marine based parts of the last Eurasian Ice Sheet

Hans Petter Sejrup, Berit Oline Hjelstuen, Mariana Ramos Esteves, Henry Patton, Monica Winsborrow, Karin Andreassen, Tine Rasmussen, and Alun Hubbard

 The timing, rates and patterns of retreat of western sectors of the last Eurasian Ice Sheet (EurIS) are poorly constrained, hampered by limited observations from the marine domain. A better knowledge of the deglaciation of the NW European marine areas/continental margins is essential for efforts to understand the role of different controlling factors (such as ice streams, atmospheric and oceanic conditions, relative sea level, morphology and substrate) on the stability of the EurIS, and also for ice-sheet stability in general. Based on new and existing mapping of glacial landforms, together with a compilation of existing and recalibrated dates from the NW European shelf, a new reconstruction of the retreating EurIS between 20 and 14 ka BP will be presented. Our reconstruction suggests an initial modest withdrawal from maximum extent to c. 19 ka BP along the entire western marine-terminating margin. From 19ka the two major marine-terminating ice streams, in the Norwegian Channel and Bear Island Trough, begin to retreat/collapse. This destabilisation leads to rapid interior downdraw and the eventual unzipping of the British-Irish and Fennoscandian ice sheets at c. 18.5 ka BP, and the Barents-Kara and Fennoscandian ice sheets between 16 and 15 ka BP. Based on our new reconstruction and modelling results, the importance of factors controlling the nonsynchronous and rapid deglaciation of marine-based sectors and the implications for the stability of the ice sheet, will be discussed. The chronology and patterns of past marine deglaciations provide contextual insight into ice sheet instabilities and the mechanisms behind, underpinning the ongoing retreat of the Greenland and Antarctic ice sheets today.

 

How to cite: Sejrup, H. P., Hjelstuen, B. O., Esteves, M. R., Patton, H., Winsborrow, M., Andreassen, K., Rasmussen, T., and Hubbard, A.: Disintegration of the marine based parts of the last Eurasian Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6995, https://doi.org/10.5194/egusphere-egu2020-6995, 2020.

EGU2020-7294 | Displays | CR2.2

Relating polarimetric radar measurements of ice fabric to ice-flow enhancement of Rutford Ice Stream

Thomas Jordan, Alex Brisbourne, Carlos Martin, Rebecca Schlegel, Dustin Schroeder, and Andrew Smith

Lateral shear margins provide resistance to ice flow within ice streams and play an important role in the overall dynamics of ice sheets. The strength and location of shear margins are known to be influenced by both subglacial factors (e.g. bed roughness, meltwater availability) and ice rheology (ice temperature, ice fabric, and damage). Assessing the relative contribution of these factors upon ice-stream flow is complex but can be aided by geophysical measurements (e.g. radar-sounding and seismic imaging) of the ice-stream subsurface. There are, however, ongoing challenges in obtaining geophysical information in an appropriate form to be incorporated into ice-flow models. This is true of ice fabric, and its direction-dependent effect upon ice viscosity is typically neglected in models of ice streams.

Here we develop a framework to relate ice fabric measurements from polarimetric radar sounding to ice-flow enhancement within ice streams. First, we extend a `polarimetric coherence’ radar method to automate the extraction of ice fabric using quad-polarized data.  Second, using a previously developed anisotropic flow-law formulation, we relate the radar fabric measurements to direction-dependent enhancement factors of glacier ice. We demonstrate the approach using a radar ground survey, collected by the British Antarctic Survey, which traverses between the centre and shear margin of Rutford Ice Stream. The data indicate that a vertical girdle fabric is present in the near-surface of the ice stream (approximately the top 300 m) which azimuthally rotates and strengthens toward the shear margin. We then assess the effect that the girdle fabric has upon shear and compression and the impact upon ice-flow models of Rutford Ice Stream.

 

 

 

How to cite: Jordan, T., Brisbourne, A., Martin, C., Schlegel, R., Schroeder, D., and Smith, A.: Relating polarimetric radar measurements of ice fabric to ice-flow enhancement of Rutford Ice Stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7294, https://doi.org/10.5194/egusphere-egu2020-7294, 2020.

EGU2020-9048 | Displays | CR2.2

Modelling ice rise englacial temperature profiles to constrain past ice-sheet dynamics

Aleksandr Montelli and Jonathan Kingslake

Present-day englacial temperatures are the product of the millennial-scale histories of ice flow and thermal boundary conditions experienced by an ice sheet. Vertical englacial temperature profiles extracted from boreholes drilled at ice divides record past ice dynamics and changing external forcings. Bindschadler (1990) estimated the timing of grounding of Crary Ice Rise, Ross Sea, by minimizing the mismatch between modelled and measured temperature profiles. This approach has huge potential if future boreholes are drilled at Antarctic ice rises in locations suspected of undergoing significant dynamics change. Yet, the uncertainties inherent in this approach must be carefully assessed to target and maximize the utility of borehole drilling. Here, using a 1D vertical heat flux model, we simulate the evolution of temperature as a function of depth in six locations with slow-flowing, cold-based ice in the Weddell and Ross Sea sectors of the West Antarctic Ice Sheet. The locations were chosen using output from the Parallel Ice Sheet Model (PISM) as which are most likely to have ungrounded and regrounded during the last deglaciation (i.e., through last 20 k.y.). We use the shallow ice approximation assuming horizontally isothermal ice and no basal sliding. Several parameters, accounting for timing and duration of grounding/ungrounding events, surface temperature evolution, accumulation rate, ice-thickness change, geothermal heat flux and vertical velocity, are varied to generate a range of different temperature profile outputs. Uncertainties associated with each parameter are then evaluated using a Monte-Carlo approach, yielding a statistical account of model sensitivity to key variables. We highlight that the precision needed to infer timing of grounding increases with the duration of grounded ice flow. Results presented here can help in choosing future ice drilling sites, and provide useful constraints on inferring past forcings and changing boundary conditions from in-situ temperature-depth measurements.

How to cite: Montelli, A. and Kingslake, J.: Modelling ice rise englacial temperature profiles to constrain past ice-sheet dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9048, https://doi.org/10.5194/egusphere-egu2020-9048, 2020.

EGU2020-9829 | Displays | CR2.2

Extending the paleoglaciological record of the southeastern Tibetan Plateau by combining geochronological and high-resolution remote sensing techniques

Arjen P. Stroeven, Ramona A.A. Schneider, Robin Blomdin, Natacha Gribenski, Marc W. Caffee, Chaolu Yi, Xiangke Xu, Xuezhen Zeng, Martina Hättestrand, Ping Fu, and Lewis A. Owen

Paleoglaciological data is a crucial source of information towards insightful paleoclimate reconstructions by providing vital boundary conditions for regional and global climate models. In this context, the Third Pole Environment is considered a key region because it is highly sensitive to global climate change and its many glaciers constitute a diminishing but critical supply of freshwater to downstream communities in SE Asia. Despite its importance, extents of past glaciation on the Tibetan Plateau remain poorly documented or controversial largely because of the lack of well define glacial chronostratigraphies and reconstructions of former glacier extent. This study contributes to a better documentation of the extent and improved resolution of the timing of past glaciations on the southeastern margin of the Tibetan Plateau. We deploy a high-resolution TanDEM-X Digital Elevation Model (12 m resolution) to produce maps of glacial and proglacial fluvial landforms in unprecedented detail. Geomorphological and sedimentological field observations complement the mapping while cosmogenic nuclide exposure dating of quartz samples from boulders on end moraines detail the timing of local glacier expansion. Additionally, samples for optically stimulated luminescence dating were taken from extensive and distinct terraces located in pull-apart basins downstream of the end moraines to determine their formation time. We compare this new dataset with new and published electron spin resonance ages from terraces. Temporal coherence between the different chronometers strengthens the geochronological record while divergence highlights limitations in the applicability of the chronometers to glacial research or in our conceptual understanding of landscape changes in tectonic regions. Results highlight our current understanding of paleoglaciation, landscape development, and paleoclimate on the SE Tibetan Plateau.

How to cite: Stroeven, A. P., Schneider, R. A. A., Blomdin, R., Gribenski, N., Caffee, M. W., Yi, C., Xu, X., Zeng, X., Hättestrand, M., Fu, P., and Owen, L. A.: Extending the paleoglaciological record of the southeastern Tibetan Plateau by combining geochronological and high-resolution remote sensing techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9829, https://doi.org/10.5194/egusphere-egu2020-9829, 2020.

EGU2020-11714 | Displays | CR2.2

Numerically simulated ice dynamics and erosion patterns under specific climate scenarios

Fabio Magrani, Pierre Valla, and David Egholm

Numerical modeling already demonstrated to be a powerful tool for investigating the role of surface processes, including glaciation, in landscape evolution. Ice model developments from 1-D simulations (Oerlemans, 1984; MacGregor et al., 2000) to more recent 2-/3D models (e.g. Egholm et al., 2011) allow investigating glacier dynamics and landscape erosion over various timescales by also incorporating the effects of rugged topography and feedbacks between erosion by glacial sliding and the extent of glaciation.

Precipitation and temperature are primary controls on glacier mass balance, driving basal sliding and erosion in response to changes in both ice thickness and extent. However, still little is known on how erosion patterns behave under temporally- and spatially-varying combinations of these two climatic parameters. Since ice basal sliding and fluctuations of water-pressure peak around the equilibrium-line altitude (ELA) (MacGregor et al., 2000; Herman et al., 2011), erosion would be expected to follow similar patterns due to their relationship with abrasion and quarrying. However, modeled glaciers with similar geographical extents may present significant differences in either ice thickness and/or ELA, depending on the simulated climate scenarios (i.e. combinations of precipitation/temperature). This will in turn affect ice dynamics and thus erosion patterns, especially differences between the accumulation and ablation areas.

In this study we aim to numerically explore how both ice dynamics and erosion patterns are influenced by specific climatic scenarios (i.e. precipitation and temperature conditions). Towards this, we used the Integrate Second Order Shallow Ice Approximation - iSOSIA (Egholm et al., 2011) model, which uses a positive degree-day (PDD) model for mass balance and a depth-integrated computation for ice flux with irregular Voronoi cell grids, allowing local mesh adjustments in selected topographic areas. In addition, this model is capable to couple ice, water and sediments which permits to explore erosion feedbacks onto ice dynamics.

Using a synthetic Alpine landscape, we performed a set of simulations with mass balance scenarios preserving similar ELAs and ice extents between runs. From these simulations, we generated glacial erosion patterns (e.g. steady-state erosion, total erosion integrated over a glacial cycle), testing different erosion laws (abrasion, quarrying) as well as the role of subglacial water and sediment entrainment. From the different scenarios, we also investigated how ice dynamics (i.e. ice flux and thickness) and erosion rates vary spatially and differ between the accumulation/ablation areas. Our ultimate goal is to understand how glacial erosion patterns, combined with classic paleo-glacial reconstructions and paleo-ELA estimates, can be used as proxies for paleoclimate reconstruction.

 

References:

Egholm, D.L. et al. (2011). Modeling the flow of glaciers in steep terrains: The integrated second‐order shallow ice approximation (iSOSIA). Journal of Geophysical Research. Vol. 116.

Herman, F. et al. (2011). Glacial hydrology and erosion patterns: A mechanism for carving glacial valleys. Earth and Planetary Science Letters. Vol. 310.

MacGregor, K.R. et al. (2000). Numerical simulations of glacial-valley longitudinal profile evolution. Geology. Vol. 28. No. 11.

Oerlemans, J. (1984). Numerical experiments on large-scale glacial erosion: Zeitschrift für Gletscherkunde und Glazialgeologie. Vol. 20.

How to cite: Magrani, F., Valla, P., and Egholm, D.: Numerically simulated ice dynamics and erosion patterns under specific climate scenarios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11714, https://doi.org/10.5194/egusphere-egu2020-11714, 2020.

EGU2020-11787 | Displays | CR2.2

Improved reconstruction of the southeastern Laurentide Ice Sheet deglaciation: constraining ice thinning using in-situ cosmogenic 10Be and 14C and critically evaluating different retreat rate chronometers

Christopher Halsted, Jeremy Shakun, Lee Corbett, Paul Bierman, P. Thompson Davis, Brent Goehring, Alexandria Koester, and Marc Caffee

In the northeastern United States, there are extensive geochronologic and geomorphic constraints on the deglaciation of the southeastern Laurentide Ice Sheet; thus, it is an ideal area for large-scale ice volume reconstructions and comparison between different ice retreat chronometers. Varve chronologies, lake and bog-bottom radiocarbon ages, and cosmogenic nuclide exposure ages constrain the timing of ice retreat, but the inferred ages exhibit considerable noise and sometimes disagree. Additionally, there are few empirical constraints on ice thinning, forcing ice volume reconstructions to rely on geophysically-based ice thickness models. Here, we aim to improve the understanding of the southeastern Laurentide Ice Sheet recession by (1) adding extensive ice thickness constraints and (2) compiling all available deglacial chronology data in the region to investigate discrepancies between different chronometers.

To provide insight about ice sheet thinning history, we collected 120 samples for in-situ 10Be and 10 samples for in-situ 14C cosmogenic exposure dating from various elevations at 13 mountains in the northeastern United States. By calculating ages of exposure at different elevations across this region, we reconstruct paleo-ice surface lowering of the southeastern Laurentide Ice Sheet during deglaciation. Where we suspect that 10Be remains from pre-Last Glacial Maximum periods of exposure, in-situ 14C is used to infer the erosional history and minimum exposure age of samples.

Presently, we have measured 10Be in 73 samples. Mountain-top exposure ages located within 150 km of the southeastern Laurentide Ice Sheet terminal moraine indicate that near-margin thinning began early in the deglacial period (~19.5 to 17.5 ka), coincident with the slow initial margin retreat indicated by varve records. Exposure ages from several mountains further inland (>400 km north of terminal moraine) collected over ~1000 m of elevation range record rapid ice thinning between 14.5 and 13 ka. Ages within each of these vertical transects are similar within 1σ internal uncertainty, indicating that ice thinned quickly, less than a few hundred years at most. This rapid thinning occurred at about the same time that varve records indicate accelerated ice margin retreat (14.6–12.9 ka), providing evidence of substantial ice volume loss during the Bølling-Allerød warm period.

Our critical evaluation of deglacial chronometers, including valley-bottom 10Be ages from this project, is intended to constrain ice margin retreat rates and timing in the region. Ultimately, we will integrate our ice thickness over time constraints with the existing network of deglacial ages to create a probabilistic reconstructions of the southeastern Laurentide Ice Sheet volume during its recession through the northeastern United States.

How to cite: Halsted, C., Shakun, J., Corbett, L., Bierman, P., Davis, P. T., Goehring, B., Koester, A., and Caffee, M.: Improved reconstruction of the southeastern Laurentide Ice Sheet deglaciation: constraining ice thinning using in-situ cosmogenic 10Be and 14C and critically evaluating different retreat rate chronometers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11787, https://doi.org/10.5194/egusphere-egu2020-11787, 2020.

EGU2020-9886 | Displays | CR2.2

Geophysical evidence for a large Holocene ice marginal moraine of Skeiðarárjökull, SE Iceland

Devin Harrison, Neil Ross, Andrew Russell, and Stuart Jones

The sedimentary record of Icelandic ice-contact environments provides valuable information about glacier margin dynamics and position, relative sea-level and the geomorphic processes driving proglacial environments. This important archive has been little exploited, however, with most glacier and sea level reconstructions based on limited sedimentary exposures and surface geomorphic evidence. Although geophysical surveys of Icelandic sandur have been conducted, they have often been of limited spatial scale and focused on specific landforms. Here, we report an extensive (42 km of data) detailed low-frequency (40 and 100 MHz) ground-penetrating radar (GPR) survey of the Sandgigúr moraine complex, SE Iceland, which transforms our understanding of this landform, with implications for the Holocene history of Skeiðarársandur and SE Iceland.

The Sandgigúr moraines are located on Skeiðarársandur, SE Iceland, down-sandur of large Little Ice Age-moraines of Skeiðarárjökull. They have a relatively subtle surface geomorphic expression (typically 125 m wide and 7 m high), and knowledge of their formation is limited, with no dating control on their age or detailed geomorphic or sedimentological investigations.  GPR investigations reveal a much larger (60 m high and 1200 m wide) and extensive buried moraine complex than that suggested by surface morphology, suggesting that the moraine was a major Holocene ice margin of Skeiðarárjökull.

GPR reflections interpreted as large progradational foresets (up to 20 m in height) beneath the morainic structure are consistent with a sub-aqueous depositional environment before moraine formation, providing potential controls on former sea-level.  The GPR data also provide information on the internal structure of the moraine, with evidence for glacitectonism within the proximal side of the moraine, multiphase moraine formation, and possible buried ice at depth. A 30-40 m thick package of down-sandur dipping GPR reflections drape the leeside of the moraine, evidencing glaciofluvial deposition during and after moraine development. Potential moraine breaches, possibly caused by glaciofluvial (e.g. jökulhlaup) events, are also apparent within the GPR data and the surface geomorphology.

We combine GPR-derived subsurface architecture with the current surface morphology to develop a conceptual model detailing the geomorphic evolution of the moraines and surrounding region, from pre-moraine morphology, to their formation and breaching, resulting in the subsequent present-day morphology. These results provide new insights into the Holocene to present-day evolution of Skeiðarársandur and Skeiðarárjökull, with implications for reconstructions of the Holocene environmental history of SE Iceland.

How to cite: Harrison, D., Ross, N., Russell, A., and Jones, S.: Geophysical evidence for a large Holocene ice marginal moraine of Skeiðarárjökull, SE Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9886, https://doi.org/10.5194/egusphere-egu2020-9886, 2020.

EGU2020-12713 | Displays | CR2.2

10Be dating Cordilleran-Laurentide ice-sheet separation during the last deglaciation

Jorie Clark, Anders Carlson, Alberto Reyes, and Glenn Milne

During the last glacial maximum, the Cordilleran and Laurentide ice sheets met just to the east of the Canadian Rocky Mountains, forming an ice-sheet saddle. When this saddle disappeared has implications on deglacial global sea-level rise and abrupt climate change as well as human migration patterns to the Americas. We will present new 10-Be boulder ages from six sites on a ~1100 km transect along the ice-sheet suture zone, to date Cordilleran-Laurentide ice-sheet separation. Results will directly test whether or not Cordilleran-Laurentide separation contributed to abrupt sea-level rise during meltwater pulse 1a (14.6-14.3 ka) in response to abrupt Bølling warming (14.6-14.0 ka).

How to cite: Clark, J., Carlson, A., Reyes, A., and Milne, G.: 10Be dating Cordilleran-Laurentide ice-sheet separation during the last deglaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12713, https://doi.org/10.5194/egusphere-egu2020-12713, 2020.

The timing of northwest Laurentide ice-sheet deglaciation is important for understanding how ice-sheet retreat, and associated meltwater discharge, may have been involved in abrupt climate change and rapid sea-level rise at the end of the last glaciation. However, the deglacial chronology across the western Canadian Shield is poorly understood, with only a handful of minimum-limiting 14C dates and sparse cosmogenic nuclide exposure dates constraining the timing and pattern of northwest Laurentide ice-sheet retreat across >1000 km of ice-sheet retreat to the marine limit west of Hudson Bay. We present cosmogenic 10Be surface exposure dating of glacial erratics at two sites, within a ~160,000 km2 region with no reliable temporal constraints on ice-margin retreat, to directly date the timing of northwest Laurentide ice-sheet deglaciation. Six erratics perched directly on bedrock at a site on the western edge of the Slave Craton have exposure ages between 12.8±0.6 and 12.2±0.6 thousand years ago (ka; ±1sigma). Five erratics on bedrock, sampled at a site 115 km up-ice to the east, yielded exposure ages between 10.8±0.5 and 11.6±0.5 ka. When corrected for decreased atmospheric depth due to isostatic uplift since deglaciation, the error-weighted mean ages for the two sites indicate that the Laurentide ice sheet retreated through this region of the western Canadian Shield between 13.3±0.2 and 11.8±0.2 ka, or at least 1 kyr earlier than inferred from the canonical compilation of minimum-limiting 14C dates for deglaciation and paleo-glaciological models. We tentatively infer a preliminary ice-margin retreat rate of ~0.1 m kyr-1 over this interval spanning much of the Younger Dryas which, compared to earlier estimates, implies a substantially lower volume of meltwater flux from the retreating northwest Laurentide ice sheet at this time.  Additional exposure ages on glacial erratics across this data-poor region are needed for validation of existing deglacial ice-sheet models, which can in turn contribute to comprehensive testing of hypotheses related to northwest Laurentide ice-sheet retreat rate, abrupt deglacial sea-level rise, and potential forcing of associated climate change events.

How to cite: Reyes, A., Carlson, A., and Reimink, J.: Revised chronology of northwest Laurentide ice-sheet deglaciation from beryllium-10 exposure-dated erratics on the western Canadian Shield, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13198, https://doi.org/10.5194/egusphere-egu2020-13198, 2020.

EGU2020-3417 | Displays | CR2.2

Submarine glacial landforms in Southeast Greenland fjords reveal contrasting outlet-glacier behaviour since the Last Glacial Maximum

Christine Batchelor, Julian Dowdeswell, Eric Rignot, and Romain Millan

The Southeast (SE) Greenland margin, which includes the SE sector of the Greenland Ice Sheet (GIS) and the eastern Julianehåb Ice Cap (JIC), is drained by a number of fast‐flowing, marine‐terminating outlet glaciers. Although the SE Greenland margin is suggested to have been highly sensitive to past climatic changes, mountainous terrain and a lack of ice‐free areas have largely prevented analysis of the deglacial and Holocene behaviour of these outlet glaciers. Here we use bathymetric data, from multibeam echo-sounding acquired by NASA’s Earth Venture Sub‐orbital Oceans Melting Greenland (OMG) mission and from gravity inversion derived from Operation Icebridge (OIB) gravity data, from 36 fjords along the SE Greenland margin to map the distribution of more than 50 major submarine moraines. The moraines are up to 3 km long in the former ice‐flow direction, reach up to 150 m above the surrounding seafloor, and span the width of the fjord.

Inner‐fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords of the SE GIS and the JIC. Their locations beyond the oldest ice‐margin position where it is known from aerial photographs and correlation with prominent terrestrial moraines suggest that the inner‐fjord moraines were produced sometime during the Neoglacial (since approximately 4 ka).

Major moraine ridges are present in a midfjord setting in all of the nine fjords of the eastern JIC yet are generally absent from the deeper and wider fjords of the SE GIS. Given the distribution of published deglacial ages, we hypothesize that the midfjord moraines of the eastern JIC were formed during an ice‐margin still‐stand or advance that occurred during the early Holocene. It is possible that this still‐stand or advance had a climatic control, for example, the 8.2‐ka event that has been recorded from Greenland ice cores. The absence of midfjord moraines from the deeper and wider fjords of the SE GIS to the north suggests relatively rapid and continuous ice retreat occurred during the last deglaciation. The contrasting behaviour of the SE GIS and the eastern JIC during the last deglaciation probably reflects differences in fjord geometry and exposure to ocean heat.

How to cite: Batchelor, C., Dowdeswell, J., Rignot, E., and Millan, R.: Submarine glacial landforms in Southeast Greenland fjords reveal contrasting outlet-glacier behaviour since the Last Glacial Maximum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3417, https://doi.org/10.5194/egusphere-egu2020-3417, 2020.

EGU2020-15076 | Displays | CR2.2

Physically-based oscillations of the Laurentide under glacial conditions.

Daniel Moreno, Javier Blasco, Jorge Álvarez-Solas, Alexander Robinson, and Marisa Montoya

The climate during the last glacial period was far from stable. Evidence has shown the presence of layers of ice-rafted debris (IRD) in deep sea sediments, which have been interpreted as quasi-periodic episodes of massive iceberg calving from the Laurentide Ice Sheet (LIS). Several mechanisms have been proposed, yet the ultimate cause of these events is still under debate. In fact, one of the main sources of uncertainty and diversity in model response is the choice of basal friction law. Therefore, it is essential to determine the impact of this feature in glacial transport and erosion, deposition of sediments and ice streams among others. We herein study the effect of a wide range of basal friction parameters and laws under glacial conditions over the LIS. In addition, the impact of the thermodynamic state of the ice is taken into account by means of two independent procedures: a two-valued friction coefficient approach and an active basal hydrology. The aim is to determine under what conditions, if any, physically-based oscillations are possible in a three-dimensional hybrid ice-sheet model. Increasing our understanding of both basal friction laws and basal hydrology will improve not only reconstructions of paleo ice dynamics but also help to constrain the potential future evolution of current ice sheets.

How to cite: Moreno, D., Blasco, J., Álvarez-Solas, J., Robinson, A., and Montoya, M.: Physically-based oscillations of the Laurentide under glacial conditions., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15076, https://doi.org/10.5194/egusphere-egu2020-15076, 2020.

EGU2020-17965 | Displays | CR2.2

New constraints on Plio-Pleistocene East Antarctic Ice Sheet thickness: cosmogenic exposure data from western Dronning Maud Land

Jane L. Andersen, Jennifer C. Newall, Robin Blomdin, Sarah E. Sams, Derek G. Fabel, Alexandria J. Koester, Finlay M. Stuart, Nathaniel A. Lifton, Ola Fredin, Marc W. Caffee, Neil F. Glasser, Irina Rogozhina, Yusuke Suganuma, Jonathan M. Harbor, and Arjen P. Stroeven

Reconstructing past ice surface changes is key to test and improve ice-sheet models. Yet, data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past and future climate changes. Here, we attempt to test whether the ice-sheet margin in western Dronning Maud Land has thinned since the last glacial maximum or whether it perhaps thickened in places due to increased precipitation associated with warmer climates. We report cosmogenic multi-nuclide (10Be, 26Al, 36Cl, 21Ne) data from bedrock and erratics on nunataks along Jutulstraumen ice stream and the Penck Trough in western Dronning Maud Land, East Antarctica. Spanning elevations between 751-2387 m above sea level, and between 5 and 450 m above the contemporaneous local ice sheet surface, the samples record apparent exposure ages between 2 ka and 5 Ma. The highest bedrock sample indicates (near-) continuous exposure since at least the Pliocene, with a very low apparent erosion rate of 15±3 cm Ma-1. However, there are also clear indications of a thicker-than-present ice sheet within the last glacial cycle, thinning ~35-120 m at several nunataks during the Holocene (~2-11 ka). Owing to difficulties in retrieving suitable sample material from the often rugged and quartz-poor mountain summits, and due to the presence of inherited nuclides in many of our samples, we are unable to present robust thinning estimates from elevational profiles. Nevertheless, the results clearly indicate ice-surface fluctuations of several hundred meters within the last glacial cycle in this sector of the EAIS, between the current grounding line and the edge of the polar plateau. Finally, inverse modelling of the cosmogenic multi-nuclide inventories in bedrock yields estimates of total erosion and ice cover across multiple glacial cycles. Our results show that the EAIS in western Dronning Maud Land was thicker than present during most of the Quaternary, covering sample sites up to 200 m above the present-day ice sheet for ~80 % of this period. Thinning of the ice since the last glacial maximum, combined with a long-term record of thicker-than-present ice, indicate that the ice sheet below the polar plateau in western Dronning Maud Land generally expands and thickens during climate cooling, despite decreasing precipitation associated with a cooler Southern Ocean.

How to cite: Andersen, J. L., Newall, J. C., Blomdin, R., Sams, S. E., Fabel, D. G., Koester, A. J., Stuart, F. M., Lifton, N. A., Fredin, O., Caffee, M. W., Glasser, N. F., Rogozhina, I., Suganuma, Y., Harbor, J. M., and Stroeven, A. P.: New constraints on Plio-Pleistocene East Antarctic Ice Sheet thickness: cosmogenic exposure data from western Dronning Maud Land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17965, https://doi.org/10.5194/egusphere-egu2020-17965, 2020.

EGU2020-19779 | Displays | CR2.2

How much can we benefit from the combination of numerical simulation and in situ observations? A case study on an Arctic polythermal valley glacier

Songtao Ai, Zemin Wang, Jiachun An, Yuande Yang, Chunxia Zhou, Tingting Liu, Hao Ke, Weifeng Hao, and Hong Geng

Ice flow velocity is sensitive to glacier variations both controlling and representing the delivery of ice and affecting the future stability of ice masses in a warming climate. Austre Lovénbreen (AL) is one of the poly-thermal glaciers in the high Arctic and located on the northwestern coast of Spitsbergen, Svalbard. The ice flow velocity of AL was investigated using in situ global positioning system (GPS) observations over 15 years and numerical modelling with Elmer/Ice. First, the ice flow velocity field of AL along central flow line was presented. While AL moves slowly at a speed of approximate 4 m/a, obvious seasonal changes of ice flow velocity can be found in the middle of the glacier, where the velocity in spring-summer is 47% larger than in autumn–winter in 2016, and the mean annual velocity variation in different seasons is 14% from 2009 until 2016. Second, the numerical simulation was performed considering the poly-thermal character of the glacier, and indicated that there are two peak ice flow regions on the glacier, and not just one peak ice flow region as previously believed. The new peak ice flow zone found by simulation was verified by field work, which also demonstrated that the velocity of the newly identified zone is 8% faster than the previously identified zone. Third, although our field observations showed that the ice flow velocity is slowly increasing recently, the maximum ice flow velocity will soon begin to decrease gradually in the long term according to glacier evolution modelling of AL.

How to cite: Ai, S., Wang, Z., An, J., Yang, Y., Zhou, C., Liu, T., Ke, H., Hao, W., and Geng, H.: How much can we benefit from the combination of numerical simulation and in situ observations? A case study on an Arctic polythermal valley glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19779, https://doi.org/10.5194/egusphere-egu2020-19779, 2020.

EGU2020-6774 | Displays | CR2.2

Asynchronous instability of NE ice streams of the Laurentide Ice Sheet recorded in the marine sediments of Labrador Sea during the last glacial cycle

Harunur Rashid, Mary Smith, Min Zeng, Yang Wang, Julie Drapeau, and David Piper

Hughes et al. (1977) hypothesized of a pan-Arctic Ice Sheet that behaved as a single dynamic system during the Last Glacial Maximum. Moreover, the authors suggested a nearly grounded ice shelf in Davis Strait implying that little or no exchange between Baffin Island and the Labrador Sea. Here we present data at 1-cm (<100 years) resolution between ~12 ka and 45 ka that shed light on the discharge from Hudson Strait and Lancaster Sound ice streams of the Late Pleistocene Laurentide Ice Sheet. A reference sediment core at 938 m water depth on the SE Baffin Slope was investigated with new oxygen isotope stratigraphy, X-ray fluorescence geochemistry, and 18 14C-AMS dates and correlated to 14 regional deep-water cores. Detrital carbonate-rich sediment layers H0-H4 were derived principally from Hudson Strait. Shortly after H2 and H3, the shelf-crossing Cumberland Sound ice stream supplied dark brown ice-proximal stratified sediments but no glacigenic debris-flow deposits. The counterparts of H3, H4, and (?)H5 events in the deep Labrador basin are 4–10 m thick units of thin-bedded carbonate-rich mud turbidites from glacigenic debris flows on the Hudson Strait slope. The behavior of the Hudson Strait ice stream changed through the last glacial cycle. The Hudson Strait ice stream remained at the shelf break in H3-H5 but retreated rapidly across the shelf in H0-H2 and did not deglaciate Hudson Bay. During this time, Cumberland Sound ice twice reached the shelf edge. In H3–H5, it remained at the shelf break long enough to supply thick turbidites. Minor supply of carbonate-rich sediment from Baffin Bay allows chronologic integration of the Baffin Bay and Labrador Sea detrital carbonate records, which is diachronous with respect to Heinrich events. The asynchrony of the carbonate events implies an open seaway through Davis Strait. Our data suggest that the maximum extent of ice streams in Hudson Strait, Cumberland Sound, and Lancaster Sound was neither synchronous.

How to cite: Rashid, H., Smith, M., Zeng, M., Wang, Y., Drapeau, J., and Piper, D.: Asynchronous instability of NE ice streams of the Laurentide Ice Sheet recorded in the marine sediments of Labrador Sea during the last glacial cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6774, https://doi.org/10.5194/egusphere-egu2020-6774, 2020.

It is classically assume that prior to deep glacial valleys incision below large scale ice cap, often interpreted as the results of ice flow melting during tidewater period, the initial glacial topography was flat or very low angle and created during a major phase of cold glaciers advance as suggested by quaternary studies. Therefore up to now we have assume that the top of late Ordovician buried hills separating major glacial valleys was the remains of this flat surface truncating the pre-glacial Ordovician Hawaz series, later on flooded by the Lower Silurian. Surprisingly by reinterpreting 3D seismic cubes using spectral decomposition technics on the Murzuk basin in SE Libya, it appears that the top of buried hills are not at all characterized by a flat erosional surface, but it is strongly irregular and shows the development of narrow valley networks displaying the classical dendritic erosional pattern diagnostic of fluvial erosion. These small valleys are organized into a tributary network and don’t flow toward the ice margin, i.e. toward the N-NW but most of the time flow at right angle toward the adjacent main glacial valleys which are pointing toward the NW. These narrow valley networks in this context could be either glacial tunnel valleys located at the periphery of the ice cap in close relationships with glacial fronts (their common settings) or could correspond to fluvial valleys developed later on, in a subaerial setting at some distance from glacial fronts; we retain this second interpretation because in addition to the geomorphic features: (1) they flow parallel to the fronts that we have already recognized, Moreau et al. (2005), Rubino et al.  2007 and (2) they are suspended in the sense that these lateral networks do not reach the bottom of the main glacial valley but, they appear to be connected within the upper part of the glacial infill, immediately below the early Silurian post glacial flooding characterized by the well-known Rhuddanian hot shales. As a result, the incision of the valley network appears quite late in the ice cap melting history. It is why we tend to interpret these valleys erosion as the result of post glacial melting during ice retreat at some distance from the ice front and strongly enhanced by isostatic rebound. Some possible modern analogs of such valley fringing highs may exist in Artic Canadian islands.

How to cite: Rubino, J.-L., Larcher, C., and Bourget, J.: Fluvial incised networks on top of late Ordovician interglacial valley buried hills as the result of post glacial isostatic rebound; 3D seismic input, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21838, https://doi.org/10.5194/egusphere-egu2020-21838, 2020.

EGU2020-570 | Displays | CR2.2

The deglaciation of the northwestern Laurentide Ice Sheet in the Mackenzie Mountains

Benjamin J. Stoker, Martin Margold, Duane G. Froese, and John C. Gosse

The northwestern sector of the Laurentide Ice Sheet coalesced with the Cordilleran Ice Sheet over the southern Mackenzie Mountains, and with local montane glaciers along the eastern slopes of the Mackenzie Mountains. Recent numerical modelling studies have identified rapid ice sheet thinning in this region as a major contributor to Meltwater Pulse 1A. Despite advances in remote sensing and numerical dating methods, the configuration and chronology of the northwestern sector of the Laurentide Ice Sheet has not been reconstructed in detail. The last available studies date back to the 1990s, where field surveys and mapping from aerial imagery were used to reconstruct the Last Glacial Maximum glacier extents in the Mackenzie Mountains. Cross-cutting relationships between glacial landforms and a series of 36Cl cosmogenic nuclide dates were used to propose a deglacial model involving a significant ice readvance in the region. However, the chronological evidence supporting the readvance is uncertain because the individual ages are few and poorly clustered. Here we present an updated map of the Last Glacial Maximum glacial limits and the recessional record in the Mackenzie Mountains, based on glacial geomorphological mapping from the ArcticDEM. Sixteen new 10Be dates from four sites that were previously glaciated by the Laurentide Ice Sheet constrain the deglacial sequence across the region. These dates indicate ice sheet detachment from the eastern Mackenzie Mountains at ~16 ka as summits became ice-free. The Mackenzie Valley at ~ 65 °N became ice free at ~ 13 – 14 ka, towards the end of the Bølling-Allerød warm period. These chronological constraints on the deglaciation of the Laurentide Ice Sheet allow us to reinterpret landform relationships in the Mackenzie Mountains to reconstruct the ice sheet retreat pattern. Our updated model of the LGM extent and timing of deglaciation in the Mackenzie Mountains provides important constraints for quantifying past sea level contributions and numerical modelling studies.

How to cite: Stoker, B. J., Margold, M., Froese, D. G., and Gosse, J. C.: The deglaciation of the northwestern Laurentide Ice Sheet in the Mackenzie Mountains, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-570, https://doi.org/10.5194/egusphere-egu2020-570, 2020.

EGU2020-9592 | Displays | CR2.2

Simulations of dated radiostratigraphy for the Greenland ice sheet

Andreas Born and Alexander Robinson

As layers of accumulated snow compact into ice and start to flow under its own weight, their deformations are recorded in the vertical structure of the glacier. Therefore, the isochronal stratigraphy of the Greenland ice sheet provides comprehensive dynamic constraints, which, with adequate methods, can be used to calibrate ice sheet models and greatly improve their accuracy.

We present the first three-dimensional ice sheet model that explicitly resolves isochrones. Individual layers of accumulation do not exchange mass with each other as the flow of ice deforms them, resembling the Lagrangian description of flow in the vertical dimension, while lateral flow within each layer is Eulerian. Direct comparison with dated radiostratigraphy is used to filter an ensemble of simulations of the Greenland ice sheet. The abundant information implied by the shape of the three-dimensional layering enables us to constrain a large number of degrees of freedom. The mismatch in the thickness of certain isochrones is used to calibrate the climate forcing of different periods of the last glacial cycle.

How to cite: Born, A. and Robinson, A.: Simulations of dated radiostratigraphy for the Greenland ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9592, https://doi.org/10.5194/egusphere-egu2020-9592, 2020.

EGU2020-10033 | Displays | CR2.2

Effect of Improved Bedrock Geometry on Antarctic Vulnerability to Regional Ice Shelf Collapse

Daniel Martin, Stephen Cornford, and Esmond Ng

The Antarctic Ice Sheet (AIS) is vulnerable to the thinning or even the collapse of its floating ice shelves, which tend to buttress ice streams. Any reduction in buttressing results in acceleration and thinning upstream and potentially the onset of Marine Ice Sheet Instability. Recent work demonstrates that West Antarctica is vulnerable to sustained disintegration in any of its major marine outlets, resulting in 2-3 m sea level rise over 1000 years. At the same time regions in East Antarctica are vulnerable only to the loss of local ice shelves. However, most of this work has used the Bedmap2 dataset as a starting point. Since the release of Bedmap2 in 2012, there has been a sustained campaign of observations, along with improved interpolation techniques based on mass conservation. The resulting datasets, including the recently released BedMachine dataset, incorporate much-improved bedrock and thickness data compared to what was available in Bedmap2. 

We reproduce our previous examination of the millennial-scale vulnerability of the AIS to the loss of its shelves to examine the effect of this improvement on projected Antarctic vulnerability, paying special attention to regions like the Aurora Basin which were under-constrained in Bedmap2.

How to cite: Martin, D., Cornford, S., and Ng, E.: Effect of Improved Bedrock Geometry on Antarctic Vulnerability to Regional Ice Shelf Collapse, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10033, https://doi.org/10.5194/egusphere-egu2020-10033, 2020.

EGU2020-1189 | Displays | CR2.2

Morphology reveals deglaciation patterns of the Laurentide Ice Sheet in the Clyde Inlet fjord-cross-shelf trough system, eastern Baffin Island (Arctic Canada)

Pierre-Olivier Couette, Patrick Lajeunesse, Boris Dorschel, Catalina Gebhardt, Dierk Hebbeln, Etienne Brouard, and Jean-François Ghienne

The maximal extent and subsequent deglaciation of the Laurentide Ice Sheet (LIS) across eastern Baffin Island during the last glacial cycle (MIS-2) has been widely debated during the last decades as different palaeo-glaciological models have been proposed. Spatial and temporal variability of ice sheets extension during Quaternary glaciations complicate the establishment of a reliable reconstruction of the ice dynamics in the area. Furthermore, the lack of geophysical data in most of the fjords, and seaward, makes it difficult to reconcile the proposed terrestrial and marine glacial margins. High-resolution swath-bathymetric data, collected between 2003 and 2017, display a diversity of glacial bedforms in the Clyde Inlet fjord-cross-shelf-trough system (Eastern Baffin Island, Arctic Canada). These bedforms reveal a potential position of the LIS margin during the Last Glacial Maximum (LGM) near the shelf break. Early deglaciation of the Clyde Trough was marked by an initial break up of the ice sheet. This rapid retreat of the ice margin was punctuated by episodic stabilizations forming GZWs. This retreat was followed by a readvance and subsequent slow retreat of the LIS, as indicated by the presence of recessional moraines. Long-term stabilizations within the trough possibly coincided with major climatic cooling episodes, such as the end of Heinrich event 1 (H1) and the Younger Dryas. However, these stabilizations appear to have been influenced by topography, as GZWs can be found at pinning points in the trough. Deglaciation of the fjord occurred during the early Holocene and was faster, probably due to increased water depths. The presence of multiple moraine systems however indicate that deglaciation of Clyde Inlet was marked by stages of ice margin stabilization.

How to cite: Couette, P.-O., Lajeunesse, P., Dorschel, B., Gebhardt, C., Hebbeln, D., Brouard, E., and Ghienne, J.-F.: Morphology reveals deglaciation patterns of the Laurentide Ice Sheet in the Clyde Inlet fjord-cross-shelf trough system, eastern Baffin Island (Arctic Canada), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1189, https://doi.org/10.5194/egusphere-egu2020-1189, 2020.

EGU2020-2384 | Displays | CR2.2

Late-Pleistocene geomorphological and geochronological history of the former Patagonian Ice Sheet in north-eastern Patagonia (43°S)

Tancrede P.M Leger, Andrew S. Hein, Angel Rodes, Robert G. Bingham, and Derek Fabel

The former Patagonian Ice Sheet was the most extensive Quaternary ice sheet of the southern hemisphere outside of Antarctica. Against a background of Northern Hemisphere-dominated ice volumes, it is essential to document how the Patagonian Ice Sheet and its outlet glaciers fluctuated throughout the Quaternary. This information can help us investigate the climate forcing mechanisms responsible for ice sheet fluctuations and provide insight on the causes of Quaternary glacial cycles at the southern mid-latitudes. Moreover, Patagonia is part of the only continental landmass that fully intersects the precipitation-bearing southern westerly winds and is thus uniquely positioned to study past climatic fluctuations in the southern mid-latitudes. While Patagonian palaeoglaciological investigations have increased, there remains few published studies investigating glacial deposits from the north-eastern sector of the former ice sheet, between latitudes 41°S and 46°S. Palaeoglaciological reconstructions from this region are required to understand the timing of late-Pleistocene glacial expansion and retreat, and to understand the causes behind potential latitudinal asynchronies in the glacial records throughout Patagonia. Here, we reconstruct the glacial history and chronology of a previously unstudied region of north-eastern Patagonia that formerly hosted the Rio Huemul and Rio Corcovado (43°S, 71°W) palaeo ice-lobes. We present the first detailed glacial geomorphological map of the valley enabling interpretations of the region’s late Quaternary glacial history. Moreover, we present new cosmogenic 10Be exposure ages from moraine boulders, palaeolake shoreline surface cobbles and ice-moulded bedrock. This new dataset establishes a high-resolution reconstruction of the local LGM through robust dating of five distinct moraines limits of the Rio Corcovado palaeo-glacier. Our results demonstrate that, in its north-eastern sector, the Patagonian Ice Sheet reached its last maximum extent during MIS 2, thus contrasting with the MIS 3 maxima found for the southern parts of the ice sheet. We also present geomorphological evidence along with chronological data for the formation of two ice-dammed proglacial lake phases in the valley caused by LGM ice-extent fluctuations and final glacial recession. Furthermore, this dataset allows us to determine the timing and onset of glacial termination 1 in the region. Finally, our findings include the reconstruction of a proglacial lake drainage and Atlantic/Pacific drainage reversal event caused by ice sheet break-up in western Patagonia. Such findings have significant implications for climate fluctuations at the southern mid-latitudes, former Southern Westerly Winds behaviour and interhemispheric climate linkages during and following the local LGM. They provide further evidence supporting the proposed latitudinal asynchrony in the timing of expansion of the Patagonian Ice Sheet during the last glacial cycle and enable glacio-geomorphological interpretations for the studied region.

How to cite: Leger, T. P. M., Hein, A. S., Rodes, A., Bingham, R. G., and Fabel, D.: Late-Pleistocene geomorphological and geochronological history of the former Patagonian Ice Sheet in north-eastern Patagonia (43°S), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2384, https://doi.org/10.5194/egusphere-egu2020-2384, 2020.

CR2.4 – Big Data, Machine Learning and Artificial Intelligence in Glaciology

EGU2020-9723 | Displays | CR2.4

Glacier evolution modelling with deep learning: challenges and opportunities

Jordi Bolibar, Antoine Rabatel, Isabelle Gouttevin, Clovis Galiez, Thomas Condom, and Eric Sauquet
Glacier surface mass balance (SMB) and glacier evolution modelling have traditionally been tackled with physical/empirical methods, and despite some statistical studies very few efforts have been made towards machine learning approaches. With the end of this past decade, we have witnessed an impressive increase in the available amount of data, mostly coming from remote sensing products and reanalyses, as well as an extensive list of open-source tools and libraries for data science. Here we introduce a first effort to use deep learning (i.e. a deep artificial neural network) to simulate glacier-wide surface mass balance at a regional scale, based on direct and remote sensing SMB data, climate reanalysis and multitemporal glacier inventories. Coupled with a parameterized glacier-specific ice dynamics function, this allows us to simulate the evolution of glaciers for a whole region. This has been developed as the ALpine Parameterized Glacier Model (ALPGM), an open-source Python glacier evolution model. To illustrate this data science approach, we present the results of a glacier-wide surface mass balance reconstruction of all the glaciers in the French Alps from 1967-2015. These results were analysed and compared with all the available observations in the region as well as another physical/empirical SMB reconstruction study. We observe some interesting differences between the two SMB reconstructions, which further highlight the interest of using alternative methods in glacier modelling. Due to (relatively) recent advances in data availability and open tools (e.g. Tensorflow, Keras, Pangeo) this research field is ripe for progress, with many interesting challenges and opportunities lying ahead. To conclude, some perspectives on data science glacier modelling are discussed, based on the limitations of our current approach and on upcoming tools and methods, such as convolutional and physics-informed neural networks. 

How to cite: Bolibar, J., Rabatel, A., Gouttevin, I., Galiez, C., Condom, T., and Sauquet, E.: Glacier evolution modelling with deep learning: challenges and opportunities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9723, https://doi.org/10.5194/egusphere-egu2020-9723, 2020.

EGU2020-1212 | Displays | CR2.4

A Random-Forest approach to predicting preferential-flow snowpack runoff: early results and outlook for the future

Ryan Johnson, Carlos Oroza, Francesco Avanzi, Yamaguchi Satoru, Hiroyuki Hirashimia, and Tessa Maurer

Predicting the occurrence of preferential-flow snowpack runoff as opposed to spatially homogeneous matrix flow has recently become an important topic of cryosphere research, because of its implications for better understanding and forecasting wet-snow avalanche formation, streamflow generation during rain-on-snow events, and the polar-sheet water balance. Using twelve seasons of daily data from nine multi-compartment snow-lysimeters and concurrent weather and snowpack observations, we explored the accuracy of a machine-learning algorithm, Random Forest, in predicting the occurrence of preferential-flow snowpack runoff in a maritime context where sub-freezing conditions are rare (Nagaoka, Niigata prefecture, Japan). The algorithm was trained to predict three metrics of preferential-flow snowpack runoff: the coefficient of variation and standard and maximum deviations from mean spatial snowpack runoff. Two validation scenarios were used: one in which data were randomly subsampled from the entire period of record (66% training data, 33% testing), and a leave-one-year-out scenario, in which the model was trained on 11 years and tested on an unseen year. The latter was intended to represent a more realistic scenario in which limited data are available. Five tiers of features were used as inputs (independent variables) to the algorithm, including concurrent weather and bulk-snow properties, snow-atmosphere energy-balance components, internal snow structure, simulated matrix-flow snowpack runoff, and a selection of the five most important features from all previous groups. Relatively high model performance (Nash-Sutcliffe-Efficiency, NSE, > 0.53) was observed in all all-year scenarios, whereas the leave-one-year-out scenario displayed nearly a 50% reduction in performance, indicative of an inconsistent relationship across weather, snow conditions, and preferential-flow snowpack runoff generation between seasons. Random Forest also underestimated seasonal peaks in preferential flow, indicative of under-sampling in the dataset or unrepresented processes exceeding the spatial scale of multi-compartment lysimeters. This research presents an initial framework for understanding key factors influencing preferential-flow occurrence; improvements in algorithm accuracy could support predictions of preferential-flow snowpack runoff, especially in sparsely monitored regions.

How to cite: Johnson, R., Oroza, C., Avanzi, F., Satoru, Y., Hirashimia, H., and Maurer, T.: A Random-Forest approach to predicting preferential-flow snowpack runoff: early results and outlook for the future, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1212, https://doi.org/10.5194/egusphere-egu2020-1212, 2020.

EGU2020-11237 | Displays | CR2.4

IcePicks: a collaborative database of Greenland outlet glacier termini

Sophie Goliber, Taryn Black, and Ginny Catania

Marine-terminating outlet glacier terminus change mapped from satellite and aerial imagery in Greenland is used extensively in understanding how outlet glaciers adjust to climatic changes over a range of time scales. Numerous studies have digitized termini manually, but this process is labor-intensive and may lead to duplication of efforts. Additionally, these studies use different methods to pick the front (e.g. centerline pick, whole delineation, box method), which makes them difficult to compare. At the same time, machine learning techniques are rapidly making progress in their ability to accurately automate the extraction of glacier termini, with promising developments across a number of satellite sensors. However, limitations still exist: in particular, further high-quality manually-digitized training data are needed to make robust automatic picks. Here we present efforts to produce a database of manually digitized terminus picks and an intercomparison of picking techniques to determine errors and best practices for future efforts in digitization. These data will be cleaned, associated with appropriate metadata, and compiled so they can be easily accessed by scientists. Ultimately, these data will be used to create training data for further automatic picking efforts. We hope to solicit further collaboration with members of EGU and encourage those interested to email the authors.

How to cite: Goliber, S., Black, T., and Catania, G.: IcePicks: a collaborative database of Greenland outlet glacier termini, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11237, https://doi.org/10.5194/egusphere-egu2020-11237, 2020.

EGU2020-4486 | Displays | CR2.4

Deep learning reveals seasonal patterns of Antarctic ice shelf front fluctuations

Celia A. Baumhoer, Andreas J. Dietz, Mariel Dirscherl, and Claudia Kuenzer

The Antarctic ice sheet drains ice through its peripheral ice shelves and glaciers making them an important factor for ice sheet mass balance. The extent of ice shelves and their calving front position influences ice sheet discharge and can yield valuable information on ice dynamics. Moreover, glacier fronts can have strong seasonal variations of retreat and advance. Yet, little is known about the seasonal pattern of Antarctic calving front fluctuations and their effect on ice sheet dynamics. The current developments in remote sensing and big data processing allow accurate monitoring of the Antarctic coastline. But to derive monthly calving front positions, the traditional approach of manual delineation is too time-consuming to cope with the temporal and spatial abundance of contemporary satellite missions. To create an up to date monitoring of changes in the Antarctic coastline a fully-automated approach is necessary. Automation of ice front delineation is a very challenging task as conventional edge detection methods fail due to the very low contrast between shelf ice and sea ice. Therefore, to exploit the abundance of available Sentinel-1 imagery over Antarctica, we created an automated workflow to extract monthly ice shelf front positions from Sentinel-1 imagery. The core of our processing chain is the deep learning architecture U-Net trained with about 44.000 image tiles covering parts of the Antarctic coastline during various seasons. Post-processing allows generating shapefiles of front positions and creating time series of seasonal ice shelf front fluctuations. We demonstrate our proposed method on selected ice shelves along the West and East Antarctic coastline and present intra-annual changes of calving front positions. This allows us to investigate seasonal change patterns of Antarctic ice shelves between 2014 and 2019 (depending on Sentinel-1 data availability) and to obtain a better picture on current Antarctic ice shelf front dynamics.

How to cite: Baumhoer, C. A., Dietz, A. J., Dirscherl, M., and Kuenzer, C.: Deep learning reveals seasonal patterns of Antarctic ice shelf front fluctuations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4486, https://doi.org/10.5194/egusphere-egu2020-4486, 2020.

EGU2020-19357 | Displays | CR2.4

Glacier Front Detection at Tidewater Glaciers from Radar Images

AmirAbbas Davari, Thorsten Seehaus, Matthias Braun, and Andreas Maier

Glacier and ice sheets are currently contributing 2/3 of the observed global sea level rise of about 3.2 mm a-1. Many of these glaciated regions (Antarctica, sub-Antarctic islands, Greenland, Russian and Canadian Arctic, Alaska, Patagonia), often with ocean calving ice front. Many glaciers on those regions show already considerable ice mass loss, with an observed acceleration in the last decade [1]. Most of this mass loss is caused by dynamic adjustment of glaciers, with considerable glacier retreat and elevation change being the major observables. The continuous and precise extraction of glacier calving fronts is hence of paramount importance for monitoring the rapid glacier changes. Detection and monitoring the ice shelves and glacier fronts from optical and Synthetic Aperture Radar (SAR) satellite images needs well-identified spectral and physical properties of glacier characteristics.

Earth Observation (EO) is producing massive amounts of data that are currently often processed either by the expensive and slow manual digitization or with simple unreliable methods such as heuristically found rule-based systems. As it was mentioned earlier, due to the variable occurrence of sea ice, icebergs and the similarity of fronts to crevasses, exact mapping of the glacier front position poses considerable difficulties to existing algorithms. Deep learning techniques are successfully applied in many tasks in image analysis [2]. Recently, Zhang et al. [3] adopted the state-of-the-art deep learning-based image segmentation method, i.e., U-net [4], on TerraSAR-X images for glacier front segmentation. The main motivation in using SAR modality instead of the optical aerial imagery is the capability of the SAR waves to penetrate cloud cover and its all year acquisition.

We intend to bridge the gap for a fully automatic and end-to-end deep learning-based glacier front detection using time series SAR imagery. U-net has performed extremely well in image segmentation, specifically in medical image processing community [5]. However, it is a large and complex model and is rather slow to train. Fully Convolutional Network (FCN) [6] can be considered as architecturally less complex variant of U-net, which has faster training and inference time. In this work, we will investigate the suitability of FCN for the glacier front segmentation and compare their performance with U-net. Our preliminary results on segmenting the glaciers demonstrate the dice coefficient of 92.96% by FCN and 93.20% by U-net, which essentially indicate the suitability of FCN for this task and its comparable performance to U-net.

 

References:

[1] Vaughan et al. "Observations: cryosphere." Climate change 2103 (2013): 317-382.

[2] LeCun et al. "Deep learning." nature 521, no. 7553 (2015): 436.

[3] Zhang et al. "Automatically delineating the calving front of Jakobshavn Isbræ from multitemporal TerraSAR-X images: a deep learning approach." The Cryosphere 13, no. 6 (2019): 1729-1741.

[4] Ronneberger et al. "U-net: Convolutional networks for biomedical image segmentation." MICCAI 2015.

[5] Vesal et al. "A multi-task framework for skin lesion detection and segmentation." In OR 2.0 Context-Aware Operating Theaters, Computer Assisted Robotic Endoscopy, Clinical Image-Based Procedures, and Skin Image Analysis, 2018.

[6] Long et al. "Fully convolutional networks for semantic segmentation." CVPR 2015.

How to cite: Davari, A., Seehaus, T., Braun, M., and Maier, A.: Glacier Front Detection at Tidewater Glaciers from Radar Images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19357, https://doi.org/10.5194/egusphere-egu2020-19357, 2020.

EGU2020-19996 | Displays | CR2.4

Automated image classification of outlet glaciers in Greenland using deep learning

Melanie Marochov, Patrice Carbonneau, and Chris Stokes

In recent decades, a wealth of research has focused on elucidating the key controls on the mass loss of the Greenland Ice Sheet and its response to climate forcing, specifically in relation to the drivers of spatio-temporally variable outlet glacier change. Despite the increasing availability of high-resolution satellite data, the time-consuming nature of the manual methods traditionally used to analyse satellite imagery has resulted in a significant bottleneck in the monitoring of outlet glacier change. Recent advances in deep learning applied to image processing have opened up a new frontier in the area of automated delineation of glacier termini. However, at this stage, there remains a paucity of research on the use of deep learning for image classification of outlet glacier landscapes. In this contribution, we apply a deep learning approach based on transfer learning to automatically classify satellite images of Helheim glacier, the fastest flowing outlet glacier in eastern Greenland. The method uses the well-established VGG16 convolutional neural network (CNN), and is trained on 224x224 pixel tiles derived from Sentinel-2 RGB bands, which have a spatial resolution of 10 metres. Based on features learned from ImageNet and limited training data, our deep learning model can classify glacial environments with >85% accuracy. In future stages of this research, we will use a new method originally developed for fluvial settings, dubbed ‘CNN-Supervised Classification’ (CSC). CSC uses a pre-trained CNN (in this case our VGG16 model) to replace the human operator’s role in traditional supervised classification by automatically producing new label data to train a pixel-level neural network classifier for any new image. This transferable approach to image classification of outlet glacier landscapes permits not only automated terminus delineation, but also facilitates the efficient analysis of numerous processes controlling outlet glacier behaviour, such as fjord geometry, subglacial plumes, and supra-glacial lakes.

How to cite: Marochov, M., Carbonneau, P., and Stokes, C.: Automated image classification of outlet glaciers in Greenland using deep learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19996, https://doi.org/10.5194/egusphere-egu2020-19996, 2020.

EGU2020-19979 | Displays | CR2.4

Calving Front Machine (CALFIN): Automated Calving Front Dataset and Deep Learning Methodology for East/West Greenland, 1972-2019

Daniel Cheng, Yara Mohajerani, Michael Wood, Eric Larour, Wayne Hayes, Isabella Velicogna, and Eric Rignot

We present Calving Front Machine (CALFIN), an automated method for extracting calving fronts from satellite imagery. We generate results for 66 glaciers along East/West Greenland from 1972 to 2019. We output these results as a dataset, and provide new constraints on glacial evolution over the time period. This method is uniquely robust to clouds, illumination differences, ice mélange, and Landsat-7 Scan Line Corrector errors. The current implementation offers a new opportunity to explore previous trends, and validate existing models moving forward.

This method utilizes deep learning, in the form of the Google DeeplabV3+ Xception derived CALFIN Neural Network. This approach builds on existing work by Mohajerani et al., Zhang et al., and Baumhoer et al. Additional post-processing techniques allow our method to achieve accurate and useful segmentation of raw images into Shapefile outputs. 

We achieve are often indistinguishable from the manually-curated fronts, deviating from such test data by 1 pixel (about 80 meters) or less XXX% of the time across 162 test images.

CALFIN excels among the current state of the art. We show this by performing a model inter-comparison to evaluate CALFIN's performance against existing methodologies. We also showcase CALFIN's ability to generalize to SAR and MODIS imagery. We achieve a mean error of 2.25 pixels (86.76 meters) from the true front on a diverse set of 162 testing images.

How to cite: Cheng, D., Mohajerani, Y., Wood, M., Larour, E., Hayes, W., Velicogna, I., and Rignot, E.: Calving Front Machine (CALFIN): Automated Calving Front Dataset and Deep Learning Methodology for East/West Greenland, 1972-2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19979, https://doi.org/10.5194/egusphere-egu2020-19979, 2020.

EGU2020-17780 | Displays | CR2.4

Greenland ice sheet supraglacial lake drainages between 2000 and 2019

Stephen Brough and James Lea

The drainage of supraglacial lakes provides a fundamental mechanism for the rapid transfer of surface meltwater to the bed of an ice sheet, impacting both subglacial hydrology and ice dynamics. As a consequence, it is crucial to understand where and when these lakes drain, and how or if this has changed through time. Given that lakes are now occurring in greater numbers and at higher elevations, identifying changing modes in behaviour will have significant implications for the future dynamics of the Greenland ice sheet. Nevertheless, previous studies of supraglacial lakes and associated drainage events have been limited in spatial and/or temporal scale relative to the entire ice sheet.

Here we use daily maps of Greenland wide supraglacial lake coverage – derived from MODIS Terra within Google Earth Engine – to investigate the style, pattern and timing of lake drainages between 2000 and 2019. Results from this study: i) add to the understanding of how supraglacial hydrology and its coupling to the bed has changed in response to more extensive supraglacial lake cover over the last 20 years; and ii) provide insight into how these lakes and associated drainage events can be expected to respond to increased surface meltwater production under a warming climate.

How to cite: Brough, S. and Lea, J.: Greenland ice sheet supraglacial lake drainages between 2000 and 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17780, https://doi.org/10.5194/egusphere-egu2020-17780, 2020.

EGU2020-1155 | Displays | CR2.4

High spatial and temporal resolution land surface temperature for the Antarctic Dry Valleys

Maite Lezama Valdes, Marwan Katurji, and Hanna Meyer

Anthropogenic Climate Change is expected to take a toll on the Antarctic environment and its biodiversity, which is concentrated on the continent’s few ice-free areas, such as the McMurdo Dry Valleys (MDV). To model the current terrestrial habitat distribution and predict possible climate induced changes, high spatial and temporal resolution abiotic variables, especially land surface temperature (LST) and soil moisture are needed, but are currently unavailable.

The aim of this project is to fill this gap and create a high resolution LST dataset of the Antarctic Dry Valleys. This variable is acquired in a high temporal resolution (sub-daily) by the MODIS sensor aboard Terra and Aqua satellites. However, as LST varies greatly in space, the spatial resolution provided by this data source (1000 m) is too low to give a meaningful impression of LST and to study biodiversity patterns. Therefore, we use data from Landsat and ASTER sensors as a reference to downscale MODIS LST to a spatial resolution of 30 m. 7 year’s worth of satellite data as well as terrain-derived auxiliary variables went into the development of the model, which predicts 30 m LST for the Antarctic Dry Valleys. 

To model complex relations between terrain, radiation, land cover and LST, machine learning models are used. Multiple algorithms (Random Forest, NN, SVM, Gradient Boosting) are compared to find the best approach for predicting high resolution LST based on MODIS data. Using the best performing model, a daily dataset is created that provides LST for the Antarctic Dry Valleys from 2002 on.

How to cite: Lezama Valdes, M., Katurji, M., and Meyer, H.: High spatial and temporal resolution land surface temperature for the Antarctic Dry Valleys , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1155, https://doi.org/10.5194/egusphere-egu2020-1155, 2020.

Recent advances in camera sensors, data storage, and structure-from-motion (SfM) processing are opening new possibilities for monitoring glacier processes through time series imagery. With SfM processing, internal and external camera parameters can be estimated in a bundle adjustment, alleviating problems associated with camera stability in the field. Orienting points in real world coordinates, however, still requires manual intervention in the form of ground control identification in imagery when dealing with two camera systems. We are introducing a new automated method of orienting point clouds from two-camera time lapse set ups to allow for fast processing of large numbers of frames. We accomplish this by leveraging several algorithms developed for computer vision and apply them to an analysis of glacier surface elevation change. Two time lapse systems were installed overlooking Nùłàdäy (Lowell Glacier), Yukon, Canada, on July 13, 2019. Each system consisted of a Nikon D5600 and a DigiSnap Pro, recording images at 2-hour intervals. On July 1, 2019 a manned aircraft flight collected imagery of the glacier using a Nikon D850 with a differential GPS collecting high precision locations for each image. The July 1 imagery was processed using Agisoft Photoscan Professional through the Python API to produce a target point cloud for orientation of unregistered time lapse imagery. Using Photoscan Professional’s 4D capability, a time series of images from each time lapse camera were aligned in a one-step bundle adjustment to produce a series of dense point clouds at each time step. Point clouds from time lapse imagery were coregistered to the target point cloud using a Fast Point Feature Histograms and a color-enhanced point cloud alignment based on Rusu et al. (2009) and Park et al. (2017). The M3C2 algorithm (Lague et al., 2013) was used to difference point clouds in the timeseries and derive a time series of elevation change at Nùłàdäy with an uncertainty of 1.5 m2.  All steps in the workflow are executed through Python, allowing for easy automated execution of data processing. With streamlined processing it is possible to integrate more time steps into SfM analysis of glacier surface elevation change and integrate the data into modelling efforts of glacier evolution.

How to cite: Bash, E., Dow, C., and McDermid, G.: Dealing with “too much data”: Automated Structure-from-Motion Processing of Time Lapse Imagery at Nùłàdäy Glacier, Yukon, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12949, https://doi.org/10.5194/egusphere-egu2020-12949, 2020.

EGU2020-13513 | Displays | CR2.4

BITE, the Bayesian Ice Thickness Estimation model

Mauro Werder, Matthias Huss, Frank Paul, Amaury Dehecq, and Daniel Farinotti

Accurate estimations of ice thickness and volume are indispensable for ice flow modelling, hydrological forecasts and sea-level rise projections. We present BITE, a new ice thickness estimation model based on a mass-conserving forward model and a Bayesian inversion scheme. The forward model calculates flux in an elevation-band flow-line model, and translates this into ice thickness and surface ice speed using a shallow ice formulation. Both ice thickness and speed are then extrapolated to the map plane. The model assimilates observations of ice thickness and speed using a Bayesian scheme implemented with a Markov chain Monte Carlo method, which calculates estimates of ice thickness and their error. We illustrate the model's capabilities by applying it to a mountain glacier, validate the model using 733 glaciers from four regions with ice thickness measurements, and demonstrate that the model can be used for large-scale studies by fitting it to over 30 000 glaciers from five regions. The results show that the model performs best when a few thickness observations are available; that the proposed scheme by which parameter-knowledge from a set of glaciers is transferred to others works but has room for improvements; and that the inferred regional ice volumes are consistent with recent estimates.

How to cite: Werder, M., Huss, M., Paul, F., Dehecq, A., and Farinotti, D.: BITE, the Bayesian Ice Thickness Estimation model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13513, https://doi.org/10.5194/egusphere-egu2020-13513, 2020.

CR2.6 – Remote sensing of the cryosphere

EGU2020-11363 | Displays | CR2.6

Revealing snow cover dynamics in the Hindu Kush Himalaya over the past decades

Kathrin Naegeli, Carlo Marin, Valentina Premier, Gabriele Schwaizer, Martin Stengel, Xiaodan Wu, and Stefan Wunderle

Knowledge about the snow cover distribution is of high importance for climate studies, weather forecast, hydrological investigations, irrigation or tourism, respectively. The Hindu Kush Himalayan (HKH) region covers almost 3.5 million km2 and extends over eight different countries. The region is known as ‘water tower’ as it contains the largest volume of ice and snow outside of the polar ice sheets and it is the source of Asia’s largest rivers. These rivers provide ecosystem services, the basis for livelihoods and most importantly living water for drinking, irrigation, energy production and industry for two billion people, a fourth of the world’s population, living in the mountains and downstream.

The spatio-temporal variability of snow cover in the HKH is high and studies reported average snow-covered area percentage of 10–18%, with greater variability in winter (21–42%) than in summer (2–4%). However, no study systematically investigated snow cover metrics, such as snow cover area percentage (SCA), snow cover duration (SCD) or snow cover onset (SCOD) and melt-out day (SCMD), for the entire region so far. Here, we thus present unique in-sights of regional and sub-regional snow cover dynamics for the HKH based on almost four decades, an exceptionally long and in view of the climate modelling community valuable timeseries, of satellite data obtained within the ESA CCI+ Snow project.

Our results are based on Advanced Very High Resolution Radiometer (AVHRR) data, collected onboard the polar orbiting satellites NOAA-7 to -19, providing daily, global imagery at a spatial resolution of 5 km. Calibrated and geocoded reflectance data and a consistent cloud mask pre-processed and provided by the ESA Cloud_cci project as global 0.05° composites are used. The retrieval of snow extent considers the high reflectance of snow in the visible spectra and the low reflectance values in the short-wave infrared expressed in the Normalized Difference Snow Index (NDSI). Additional thresholds related to topography and land cover are included to derive the fractional snow cover of every pixel. A temporal gap-filling was applied to mitigate the influence of clouds. Reference snow maps from high-resolution optical satellite data as well as in-situ station data were used to validate the time series.

How to cite: Naegeli, K., Marin, C., Premier, V., Schwaizer, G., Stengel, M., Wu, X., and Wunderle, S.: Revealing snow cover dynamics in the Hindu Kush Himalaya over the past decades, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11363, https://doi.org/10.5194/egusphere-egu2020-11363, 2020.

EGU2020-7348 | Displays | CR2.6

Temporal Stacking of Cross-Correlation for Glacier Offset Tracking

Shiyi Li, Philipp Bernhard, Irena Hajnsek, and Silvan Leinss

Offset tracking is one of the most widely applied methods for measuring glacier flow velocities using remote sensing data. It uses the pair-wise cross-correlation of images acquired at two different times to detect offsets between image templates of a certain size. Despite the simplicity and reliability of the method, accurate estimations of glacier velocities are limited by the accountability of features and the noise, e.g. radar speckles in synthetic aperture radar (SAR) images. One way of gaining robust estimations is to increase the size of image templates, but the resolution of obtained velocity field is inevitably depreciate. Furthermore, for templates that only contain extremely weak features with respect to the noise, increasing the size of templates is not helpful as the noise is boosted more than the features.

To overcome these issues, we propose a temporal stacking algorithm that first averages a time series of local cross-correlation functions calculated from a series of consecutive image pairs, and then estimates the averaged velocity from the stacked cross-correlation functions. Assuming the flow velocity of a glacier is constant during a certain time span (e.g. a season), the offsets between consecutive image pairs in the time series ought to be equal. Therefore, the cross-correlation functions can be considered as a time series of signals that record the identical offsets and thus are temporally coherent. Hence, we can temporally stack the signals to enhance the signal-to-noise ratio (SNR) of cross-correlation functions and better estimate offsets from the stacked cross-correlation functions. 

The proposed algorithm is assessed by mapping the flow velocity of the Aletsch Glacier using a time series of about 10 SAR images acquired by TanDEM-X in 2017 with constant revisit time of 11 days. The results show that temporal stacking of cross-correlation functions significantly enhances the spatial coverage and resolution of the obtained velocity fields compared to standard offset tracking using only pair-wise cross-correlation functions. This algorithm promotes the ability of mapping glacier velocities to a new extent with larger spatial coverage and higher spatial resolution, and provides a new perspective of measuring glacier velocities through exploiting the emerging time series data from recent high resolution space-born imaging sensors.

How to cite: Li, S., Bernhard, P., Hajnsek, I., and Leinss, S.: Temporal Stacking of Cross-Correlation for Glacier Offset Tracking, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7348, https://doi.org/10.5194/egusphere-egu2020-7348, 2020.

EGU2020-12528 | Displays | CR2.6

Gradual build up and episodic character of glacier velocity preceding and during the surge of a Karakorum glacier enabled by open-access image-processing

Ian Delaney, Saif Aati, Flavian Beaud, Shan Gremion, Surendra Adhikari, and Jean-Phillipe Avouac

Glacier surging provides a unique opportunity to examine rapid changes in glacier sliding that occur when some glaciers alternate between slower-than-normal (quiescence) and faster-than-normal (surge) velocities. On surging glaciers, mechanical instabilities within the glacier set off a regime of fast glacier flow, which causes these glaciers to accelerate and advance. The precise processes that cause a surging remain uncertain and likely vary between glaciers. However, the uptake of studies on glacier surging over the past decade continues to yield invaluable insights in glacier dynamics. In this study, we combine optical remote sensing and numerical modeling to examine the recent surge of Shishper glacier, in the Pakistani Karakorum. This glacier started surging in 2018, showed a dramatic terminus advance that reached rates of several meters per day. In the process, it dammed the adjacent valley, forming a lake which drained in June 2019 flooding the downstream valley, damaging the Karakorum Highway and threatening nearby communities. We leverage a high spatio-temporal resolution dataset of glacier velocities, using roughly 100 open-access images, across the Landsat-8 and Sentinel-2 record, thus encompassing the quiescence (2013-2018) and surge (2018-2019) phases. We created the dataset in an updated and nearly automated workflow by using the COSI-Corr software package to calculate displacements between images combined with a unique algorithm to filter data and remove artifacts. The result consists in high-resolution velocity maps with resolution with time intervals as short as five days. Such dataset provide a complete time-series of the spatio-temporal evolution of ice-surface velocities during a surge. One of the most notable finding is that the surge onset occurs progressively. In the two years leading up to the surge, spring speed-ups became increasingly larger in than the long-term median. We further identify three periods with  surge velocities far higher than the long-term median that likely coincide with hydrological events. Two periods occur in the spring (2018 and 2019) and the third corresponds with the lake formation in the winter of 2018-2019. Finally, we establish that the surge termination coincided with the lake drainage at the end of June 2019. The current availability of open-access imagery and  glacier topography allow us to  make an increased quantity of observations and thus better quantify glacier dynamics.

How to cite: Delaney, I., Aati, S., Beaud, F., Gremion, S., Adhikari, S., and Avouac, J.-P.: Gradual build up and episodic character of glacier velocity preceding and during the surge of a Karakorum glacier enabled by open-access image-processing , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12528, https://doi.org/10.5194/egusphere-egu2020-12528, 2020.

EGU2020-20908 | Displays | CR2.6

A globally complete, spatially and temporally resolved estimate of glacier mass change: 2000 to 2019

Romain Hugonnet, Robert McNabb, Etienne Berthier, Brian Menounos, Christopher Nuth, Luc Girod, Daniel Farinotti, Matthias Huss, Ines Dussaillant, Fanny Brun, and Andreas Kääb

The world’s glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology and raising global sea level. Yet, due to the scarcity of globally consistent observations, their recent evolution is only known as a heterogeneous temporal and geographic patchwork and future projections are thus not optimally constrained.

Here, we present the first globally complete, consistent and resolved estimate of glacier mass change derived from more than half a million digital elevation models (DEMs) generated or extracted from multiple satellite archives including ASTER, ArcticDEM and REMA. Combining state-of-the-art numerical photogrammetry and novel statistical approaches, we reconstruct two decades of glacier surface elevation change at an unprecedented spatial and temporal resolution. We validate our results by comparing them to independent, high-precision elevation measurements from the ICESat and IceBridge campaigns, as well as to very high resolution DEM differences from LiDAR, Pléiades, and SPOT-6. The elevation time series are integrated to volume changes for every single glacier on Earth and, by assuming an average density, aggregated to regional and global mass changes. We compare our revised glacier mass changes to earlier estimates derived from altimetry, gravimetry, geodetic and field data. As an illustration, our integrated geodetic mass loss over all Icelandic glaciers yields -8.3 +- 1.1 Gt yr-1 over the period 2002-2016 in agreement with a recent gravimetry estimate of -8.3 +- 1.8 Gt yr-1 (Wouters et al., 2019), known to perform well in this region. Both estimates are more negative than -5.7 +- 1.2 Gt yr-1, compiled from glaciological observations and geodetic data (Zemp et al., 2019).

Our global estimate of glacier mass change constitutes a new benchmark dataset that will help to: (i) assess present-day and future climate change impacts on glaciers; (ii) close the sea-level rise budget; (iii) assess the threat on water resources and (iv) facilitate research on natural hazards related to glaciers. Our results specifically provide a strong observational basis that holds a great potential to further our understanding of the multi-scale morphologic and climatic drivers of glacier mass change, essential to improve physically-based glaciological modelling and calibrate future projections.

How to cite: Hugonnet, R., McNabb, R., Berthier, E., Menounos, B., Nuth, C., Girod, L., Farinotti, D., Huss, M., Dussaillant, I., Brun, F., and Kääb, A.: A globally complete, spatially and temporally resolved estimate of glacier mass change: 2000 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20908, https://doi.org/10.5194/egusphere-egu2020-20908, 2020.

EGU2020-20874 | Displays | CR2.6

Inter-comparison of melt pond products with melt/freeze-up dates and sea ice concentration data

Sanggyun Lee, Julienne Stroeve, and Michel Tsamados

 Melt ponds are a dominant feature on the Arctic sea ice surface in summer, occupying up to about 50 – 60% of the sea ice surface during advanced melt. Melt ponds normally begin to form around mid-May in the marginal ice zone and expand northwards as the summer melt season progresses. Once melt ponds emerge, the scattering characteristics of the ice surface changes, dramatically lowering the sea ice albedo. Since 96% of the total annual solar heat into the ocean through sea ice occurs between May and August, the presence of melt ponds plays a significant role in this transfer of solar heat, influencing not only the sea ice energy balance, but also the amount of light available under the sea ice and ocean primary productivity. Given the importance melt ponds play in the coupled Arctic climate-ecosystem, mapping and quantification of melt pond variability on a Pan-Arctic basin scale are needed. Satellite-based observations are the only way to map melt ponds and albedo changes on a pan-Arctic scale. Rösel et al. (2012) utilized a MODIS 8-day average product to map melt ponds on a pan-Arctic scale and over several years. In another approach, melt pond fraction and surface albedo were retrieved based on the physical and optical characteristics of sea ice and melt ponds without a priori information using MERIS.Here, we propose a novel machine learning-based methodology to map Arctic melt ponds from MODIS 500m resolution data. We provide a merging procedure to create the first pan-Arctic melt pond product spanning a 20-year period at a weekly temporal resolution. Specifically, we use MODIS data together with machine learning, including multi-layer neural network and logistic regression to test our ability to map melt ponds from the start to the end of the melt season. Since sea ice reflectance is strongly dependent on the viewing and solar geometry (i.e. sensor and solar zenith and azimuth angles), we attempt to minimize this dependence by using normalized band ratios in the machine learning algorithms. Each melt pond retrieval algorithm is different and validation ways are different as well producing somewhat dissimilar melt pond results. In this study, we inter-compare melt ponds products from different institutes, including university of Hamburg, university of Bremen, and university college London. The melt pond maps are compared with melt onset and freeze-up dates data and sea ice concentration. The melt pond maps are evaluated by melt pond fraction statistics from high resolution satellite (MEDEA) images that have not been used for the evaluation in melt pond products. 

How to cite: Lee, S., Stroeve, J., and Tsamados, M.: Inter-comparison of melt pond products with melt/freeze-up dates and sea ice concentration data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20874, https://doi.org/10.5194/egusphere-egu2020-20874, 2020.

EGU2020-20143 | Displays | CR2.6

A merged CryoSat-2 Sentinel-3 freeboard product, its sensitivity to weather events, and what it can tell us about Ku-band radar penetration

Isobel Lawrence, Tom Armitage, Andrew Shepherd, and Michel Tsamados

The co-existence of satellite missions provides a unique opportunity for making novel observations not possible with a single satellite. Here we process data from CryoSat-2, Sentinel-3A and Sentinel-3B satellites for the 2018-19 and 2019-20 winters. Basin-average radar freeboards from Sentinel-3A/B are shown to agree with CryoSat-2 to within 3mm. A merged product is developed combining data from the CryoSat-2 and Sentinel 3A/B missions, permitting basin-wide observations of Arctic sea-level anomaly and radar freeboard at synoptic time-scales. A comparison of 9-day radar freeboard variability with snowfall data from ERA5 reanalysis reveals a strong positive correlation over first-year ice, a result which appears to contradict traditional assumptions of Ku-band radar penetration of snow. A detailed spatial analysis including a comparison of freeboard before and after the passage of storms reveals for the first time the ability to detect synoptic scale weather events in the satellite radar freeboard record.

How to cite: Lawrence, I., Armitage, T., Shepherd, A., and Tsamados, M.: A merged CryoSat-2 Sentinel-3 freeboard product, its sensitivity to weather events, and what it can tell us about Ku-band radar penetration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20143, https://doi.org/10.5194/egusphere-egu2020-20143, 2020.

EGU2020-12019 * | Displays | CR2.6 | Highlight

Farewell to IceBridge: 10 years of polar sea ice remote sensing

Linette Boisvert, Joseph MacGregor, Brooke Medley, Nathan Kurtz, Ron Kwok, Edward Blanchard-Wrigglesworth, Alek Petty, and Jeremy Harbeck

NASA’s Operation IceBridge (OIB) was a multi-year, multi-platform, airborne mission which took place between 2009-2019. OIB was designed and implemented to continue monitoring the changing sea ice and ice sheets in both the Arctic and Antarctic by ‘bridging the gap’ between NASA’s ICESat (2003–2009) and ICESat-2 (launched September 2018) satellite missions. OIB’s instrument suite most often consisted of laser altimeters, radar sounders, gravimeters and multi-spectral imagers. These instruments were selected to study polar sea ice thickness, ice sheet elevation, snow and ice thickness, surface temperature and bathymetry. With the launch of ICESat-2, the final year of OIB consisted of three campaigns designed to under fly the satellite: 1) the end of the Arctic growth season (spring), 2) during the Arctic summer to capture many different types of melting surfaces, and 3) the Antarctic spring to cover an entirely new area of East Antarctica. Over this ten-year period a coherent picture of Arctic and Antarctic sea ice and snow thickness and other properties have been produced and monitored. Specifically, OIB has changed the community’s perspective of snow on sea ice in the Arctic. Over the decade, OIB has also been used to validate other satellite altimeter missions like ESA’s CryoSat-2. Since the launch of ICESat-2, coincident OIB under flights with the satellite were crucial for measuring sea ice properties. With sea ice constantly in motion, and the differences in OIB aircraft and ICESat-2 ground speed, there can substantial drift in the sea ice pack over the same ground track distance being measured.Therefore, we had to design and implement sea ice drift trajectories based on low level winds measured from the aircraft in flight, adjusting our plane’s path accordingly so we could measure the same sea ice as ICESat-2. This was implemented in both the Antarctic 2018 and Arctic 2019 campaigns successfully. Specifically, the Spring Arctic 2019 campaign allowed for validation of ICESat-2 freeboards with OIB ATM freeboards proving invaluable to the success of ICESat-2 and the future of sea ice research to come from these missions.

 

How to cite: Boisvert, L., MacGregor, J., Medley, B., Kurtz, N., Kwok, R., Blanchard-Wrigglesworth, E., Petty, A., and Harbeck, J.: Farewell to IceBridge: 10 years of polar sea ice remote sensing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12019, https://doi.org/10.5194/egusphere-egu2020-12019, 2020.

EGU2020-22119 | Displays | CR2.6

The Ice, Cloud, and Land Elevation Satellite – 2 (ICESat-2): Mission Status, Science Results, and Outlook

Nathan Kurtz, Thomas Neumann, and Lori Magruder

The Ice, Cloud, and Land Elevation Satellite-2 has entered it’s second year on orbit, and continues to collect high-quality measurements of the changing cryosphere. The Advanced Topographic Laser Altimeter System (ATLAS) has now emitted more than 500 billion laser shots which provide elevation measurements of sea ice and the polar oceans, glaciers and ice sheets, the world’s forests, oceans, lakes and rivers in addition to vertical profiles of clouds and aerosols. ATLAS is an innovated lidar technology that utilizes low power and higher repetition rates to collect measurements every 70 cm along-track. These measurements have been shown to have high precision and accuracy comparable to or better than past and present cryospheric missions. The ICESat-2 data has also shown great promise with its ability to act as both complementary observations to many other missions as well as allow for us to extend the timeseries associated with our understanding of elevation and mass change in the polar regions. In this presentation, we will provide an update on the operations and health of the observatory, review the many available data products served through the National Snow and Ice Data Center in the US, and highlight the early science results from the mission. As of this writing, more than 2.5 million data granules have been downloaded by 1500 unique data users. Initial science papers have documented the ongoing loss of mass from the Antarctic and Greenland ice sheets, the ability of ICESat-2 to measure the seasonal changes in sea ice freeboard and thickness throughout the year, and the potential for world-wide measurements of coastal bathymetry. 

How to cite: Kurtz, N., Neumann, T., and Magruder, L.: The Ice, Cloud, and Land Elevation Satellite – 2 (ICESat-2): Mission Status, Science Results, and Outlook, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22119, https://doi.org/10.5194/egusphere-egu2020-22119, 2020.

EGU2020-16944 | Displays | CR2.6

Future impact of the Harmony InSAR satellite mission on land ice monitoring

Gert Mulder, Marcel Kleinherenbrink, Andreas Theodosiou, and Paco Lopez-Dekker

Current InSAR satellite missions have proven to be a valuable tool to monitor land ice worldwide. Applications are monitoring of glacier motion, ice/snow characteristics, but also glacier and snow type extend. Because these satellites work under all weather and lighting conditions, these missions are especially valuable in polar regions.

However, almost all current systems are restricted to repeat-pass interferometry and a single viewing geometry, limiting their use for land ice applications.

Harmony, an Earth Explorer 10 candidate mission, will strongly improve the capabilities of InSAR data for monitoring of land ice worldwide. This constellation comprises of two satellites that will fly as companions of one of the Sentinel-1 satellites. Harmony will make single-pass interferometry possible, which will be used to create improved, high-resolution digital elevation models to monitor ice mass loss. Additionally, single-pass interferometry will also provide us more details on ice and snow characteristics. Finally, every scene will be viewed from different look angles, which can enhance current ice flow estimates and allows the generation of precise three-dimensional ice motion products over the ice sheets.

In this study we show the future capabilities of the Harmony for land ice monitoring using performance models. Where possible, these models are calibrated and compared with already available Sentinel-1 data. Capabilities of the Sentinel-1 satellites for the monitoring of year-round ice movements and ice/snow characteristics are illustrated by a number of case studies.

How to cite: Mulder, G., Kleinherenbrink, M., Theodosiou, A., and Lopez-Dekker, P.: Future impact of the Harmony InSAR satellite mission on land ice monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16944, https://doi.org/10.5194/egusphere-egu2020-16944, 2020.

EGU2020-8458 | Displays | CR2.6

TanDEM-X for Cryosphere Applications

Irena Hajnsek, Georg Fischer, Giuseppe Parrella, Philipp Bernhard, and Silvan Leinss

In this presentation the focus is laid on cryospheric applications served by the single-pass interferometer TanDEM-X. The German Radar mission TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) is already successfully in operation since 2010 and is delivering continuously data over the Earth surfaces.

The main mission objective was the generation of a global and consistent digital elevation model (DEM) with a spatial resolution of 12m and a relative vertical height accuracy of 2 m. For this at least two global acquisitions where needed and innovative algorithms where developed to process the data into a global high resolution DEM. In addition to the high resolution DEM also a 90-m DEM was generated to facilitate the comparability with the former SRTM DEM. Beyond the generation of DEMs super-test sites have been establish to collect continuously data over a limited area of interest and to demonstrate and develop new algorithms to support application development. In addition TanDEM-X supports the demonstration and application of new SAR techniques, with focus on multi-static SAR, polarimetric SAR interferometry, digital beam forming and super resolution.

Today it is known through observations, delivered by satellites and conventional observing systems that the Cryosphere reacts very sensitively to climate change. However, the feedbacks to the global climate system are not well understood, impairing predictions of the impact of future climate change. Improved observational data have been provided to better quantify the main cryospheric processes and improve the representation of the Cryosphere in climate models. TanDEM-X data (product but also interferometric data) have been used from an international science team for a diversity of cryosphere applications. The presentation will provide an overview of the operation status of TanDEM-X and will focus on the applied cryopheric applications so far applied. Examples of the detection of permafrost features, the estimation of the firn-line zone, derivation of vertical ice structure, the mass loses of  over ice sheets and sea ice height estimation will be presented.

How to cite: Hajnsek, I., Fischer, G., Parrella, G., Bernhard, P., and Leinss, S.: TanDEM-X for Cryosphere Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8458, https://doi.org/10.5194/egusphere-egu2020-8458, 2020.

EGU2020-11508 | Displays | CR2.6

Detecting Greenland Melt with the SMAP L-band Radiometer

Andreas Colliander, Mohammad Mousavi, Julie Miller, Dara Entekhabi, Joel Johnson, Christopher Shuman, Zoe Courville, and John Kimball

Complex processes within the ice govern and record the evolution of the Greenland Ice Sheet. Low frequency microwave measurements have been used to gain insight into what happens deep inside the ice for some time now. NASA’s SMAP mission offers a valuable additional set of observations. SMAP covers virtually the entire ice sheet twice a day with its L-band radiometer. The overpasses center on morning and evening hours as the satellite is on a 6 AM/6PM equator-crossing orbit, and the spatial resolution of the instrument is about 40 km.

In this study, we investigated the response of L-band (1.4 GHz) measurements to surface melting of the ice sheet from the 2015 through 2019 melt seasons. The changes in brightness temperature caused by surface melt differs in the ablation zone, the active melt areas, and the interior’s dry snow zone. The melt area can be tracked with SMAP when accounting for these differences. SMAP’s frequent revisit time enables tracking of the melt events with comparatively high temporal fidelity. The evolution of the seasonal melt area derived from SMAP is consistent with other methods used for tracking ice sheet melt area.

Most notably, Greenland experienced an unusually strong melt event at the end of July 2019, which extended the melt area to the dry snow zone of the ice sheet over a period of two days. In-situ temperatures measured at Greenland’s Summit station show above-freezing temperatures during this event, and subsequent in-situ ice analyses have revealed ice structure changes associated with melt on these dates and subsequent refreezing. SMAP was able to record the extent of this unusual melt event on both days, and to show the anomalous extent of the melt event compared to the past 4 years of operational measurements.

This presentation will discuss the SMAP signal sensitivity to ice structure changes, the seasonal melt extent evolution and its inter-annual variation, and the comparison of the results to other data sources.

How to cite: Colliander, A., Mousavi, M., Miller, J., Entekhabi, D., Johnson, J., Shuman, C., Courville, Z., and Kimball, J.: Detecting Greenland Melt with the SMAP L-band Radiometer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11508, https://doi.org/10.5194/egusphere-egu2020-11508, 2020.

EGU2020-9879 | Displays | CR2.6

Antarctic Peninsula mass trends from 2003 - 2016 using a Bayesian hierarchical model approach

Stephen Chuter, Jonathan Rougier, Geoffrey Dawson, and Jonathan Bamber

Long-term continuous monitoring of Antarctic Ice Sheet mass balance is imperative to better understand its multi-decadal response to changes in climate and ocean forcing. Additionally, more accurate knowledge of contemporaneous mass balance is key for improved parameterisations in ice sheet models. The Antarctic Peninsula has undergone rapid changes in mass balance and ice dynamics over the last two decades, with satellite observations showing the presence of grounding line retreat and increases in ice sheet velocity. This is particularly the case after the collapse of the Larsen A and B ice shelves in 1995 and 2002, and more recently the glaciers draining the southern Antarctic Peninsula. As a result, this region provides analogues for future ice sheet response to ice shelf collapse in other regions of Antarctica. 

Despite the region’s importance to understanding ice sheet dynamics, it is challenging to accurately assess mass balance due its geometry and mountainous topography. Conventional pulse-limited altimetry suffers from poor coverage and data loss over steep mountainous terrain, particularly before the launch of CryoSat-2 in 2010. In the case of gravimetry, the geometry of the region means the coarse spatial resolution of the GRACE mission (~300 km) cannot resolve small spatial scale glacier changes (particularly over northern Antarctic Peninsula) and suffers from signal leakage into the ocean. For the mass budget approach, the challenge of accurately modelling surface mass balance over the region’s mountainous topography coupled with the sparsity of ice thickness observations at the grounding line for many sectors can result in large uncertainties. As a result, it can be difficult to reconcile the results from different conventional approaches in this region. 

To resolve this, we have developed and optimised the BHM framework used previously over the Antarctic Ice Sheet to specifically investigate the Antarctic Peninsula. This enables each latent process driving ice sheet mass change to be resolved at a higher spatial resolution compared to previous implementations across Antarctica as a whole. The new regional solution also incorporates more recent and higher resolution observations including: CryoSat-2 swath altimetry, stereo-image DEM differencing and NASA Operation Ice Bridge laser altimetry elevation rates. This is the first time such a range of observations of varying spatio-temporal resolutions will be combined into one assessment for the region. We will present results from the regionally optimised model from 2003 until present, including basin-scale mass trends and changes in spatial latent processes at an annual resolution. Additionally, we will discuss future opportunities, such as extending the record from this approach into the next decade and further understanding of the GIA response in this region. 

How to cite: Chuter, S., Rougier, J., Dawson, G., and Bamber, J.: Antarctic Peninsula mass trends from 2003 - 2016 using a Bayesian hierarchical model approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9879, https://doi.org/10.5194/egusphere-egu2020-9879, 2020.

EGU2020-10448 * | Displays | CR2.6 | Highlight | CR Division Outstanding ECS Lecture

Draining and Filling of an Interconnected Sub-glacial Lake Network in East Antarctica

Anna Hogg, Noel Gourmelen, Richard Rigby, and Thomas Slater

The Antarctic Ice sheet is a key component of the Earth system, impacting on global sea level, ocean circulation and atmospheric processes. Meltwater is generated at the ice sheet base primarily by geothermal heating and friction associated with ice flow, and this feeds a vast network of lakes and rivers creating a unique hydrological environment. Subglacial lakes play a fundamental role in the Antarctic ice sheet hydrological system because outbursts from ‘active’ lakes can trigger, (i) change in ice speed, (ii) a burst of freshwater input into the ocean which generates buoyant meltwater plumes, and (iii) evolution of glacial landforms and sub-glacial habitats. Despite the key role that sub-glacial hydrology plays on the ice sheet environment, there are limited observations of repeat sub-glacial lake activity resulting in poor knowledge of the timing and frequency of these events. Even rarer are examples of interconnected lake activity, where the draining of one lake triggers filling of another. Observations of this nature help us better characterise these events and the impact they may have on Antarctica’s hydrological budget, and will advance our knowledge of the physical mechanism responsible for triggering this activity. In this study we analyse 9-years of CryoSat-2 radar altimetry data, to investigate a newly identified sub-glacial network in the Amery basin, East Antarctica. CryoSat-2 data was processed in ‘swath mode’, increasing the density of elevation measurements across the study area. The plane fit method was employed in 500 m by 500 m grid cells, to measure surface elevation change at relatively high spatial resolution. We identified a network of 10 active subglacial lakes in the Amery basin. 7 of these lakes, located below Lambert Glacier, show interconnected hydrological behaviour, with filling and drainage events throughout the study period. We observed ice surface height change of up to 6 meters on multiple lakes, and these observations were validated by independently acquired TanDEM-X DEM differencing. This case study is an important decade long record of hydrological activity beneath the Antarctic Ice Sheet which demonstrates the importance of high resolution swath mode measurements. In the future the Lambert lake network will be used to better understand the filling and draining life cycle of sub-glacial hydrological activity under the Antarctic Ice Sheet.

How to cite: Hogg, A., Gourmelen, N., Rigby, R., and Slater, T.: Draining and Filling of an Interconnected Sub-glacial Lake Network in East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10448, https://doi.org/10.5194/egusphere-egu2020-10448, 2020.

EGU2020-19627 | Displays | CR2.6

CryoSat Mission and data products status after 10 years of operation

Marco Meloni, Jerome Bouffard, Tommaso Parrinello, Erica Webb, Ben Wright, Michele Scagliola, and Marco Fornari

The ESA Earth Explorer CryoSat-2 was launched on 8 April 2010 and from an altitude of just over 700 km and reaching latitudes of 88 degrees, monitors precise changes in the thickness of terrestrial ice sheets and marine ice. The aim of the CryoSat-2 mission is to determine variations in the thickness of the Earth's marine ice cover and understand the extent to which the Antarctic and Greenland ice sheets are contributing global sea level rise. In its 10 years of operations, CryoSat has achieved its mission objectives and has provided high-quality of data for a number of Earth science applications and opened up new research streams and triggered new scientific questions which have emerged from the previous phases. The purpose of this paper is to provide a general overview of the mission status and provide programmatic highlights in its new extended phase until 2021. It will also provide an overview of CryoSat data products covering both Ocean and Ice processing chains, presenting also the main evolutions and improvements that have implemented to the processors and anticipating evolutions for the future. 

 

How to cite: Meloni, M., Bouffard, J., Parrinello, T., Webb, E., Wright, B., Scagliola, M., and Fornari, M.: CryoSat Mission and data products status after 10 years of operation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19627, https://doi.org/10.5194/egusphere-egu2020-19627, 2020.

EGU2020-2751 | Displays | CR2.6

Comparison of different remote sensing methods for glacier mapping in Afghanistan

Jamal Abdul Naser Shokory and Stuart Lane

Glaciers are important sources of fresh water particularly in arid regions which have low summer precipitation. Moreover, retreating glaciers can cause serious hazards by destabilizing slopes or causing outbursts of glacial lakes. Therefore glacier monitoring is an essential task for water resources and risk management. Recently, efforts have been made to monitor glaciers using manual or semi-automated remote sensing techniques. However a particular challenge remains: as glaciers retreat they commonly develop a surface debris layer that optically is similar to zones that have not been glaciated or that are truly deglaciated: the debris cover on the glacier surface has a similar reflectance to surrounding moraines in the visible to near-infrared wavelength region. In other hand, where debris cover develops, it may insulate ice from solar radiation and diurnal temperature rises, and this will also reduce melt. Therefore, debris cover on glacier boundaries critically hinders the global inventory of glaciers. To overcome the challenges this study uses a multiple band ratio approach. The method was tested for delineating three glaciers in Afghanistan at different scales and locations to map both clean ice and debris-covered ice. We used Landsat Enhanced Thematic Mapper Plus, and a 5-meter resolution digital surface model DSM data to extract the morphological parameters. Since clean glacier ice has a high reflectivity in the visible to near-infrared wavelengths, at first we used NDIS to extract the clean ice area, but It was found that the NDSI method for glacier mapping is less sensitive to cast shadows and steep terrain. Similarly, a slope parameter has tested to map the debris cover ice area but it did not map areas with gentle slopes correctly.

Nonetheless, NIR and SWIR were identified as potential candidates for distinguishing between glaciers in shade and clean ice for the debris free case; and a combination of those bands in three different ratios and thresholds was applied successfully (Red/SWIR>= 1.5, Pan/SWIR>0.1, and NIR/SWIR>1). With regards to debris-covered ice the thermal infrared bands show potential in resolving such ambiguity, as considerable temperature differences are found to exist between debris covered ice and surrounding moraines. However, we found that thermal infrared bands have too coarse a resolution (60m) for valley glaciers. Hence, we developed a new band ratio image combining thermal infrared and panchromatic bands to better distinguish periglacial debris and supraglacial debris. This new band ratio image is given by (PAN-TIR)/(PAN+TIR), and is named as normalized supraglacial debris index (NSDI).

Accuracy assessment was carried out through comparisons of the classified maps with a manual delineation done using 1-meter high resolution RGB image with same temporal resolution. The accuracy assessment shows that the results from the proposed method are in good agreement with the manual delineation. The proposed synergistic approach therefore appears useful in the accurate mapping of debris-covered glaciers in Afghanistan.

How to cite: Shokory, J. A. N. and Lane, S.: Comparison of different remote sensing methods for glacier mapping in Afghanistan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2751, https://doi.org/10.5194/egusphere-egu2020-2751, 2020.

EGU2020-4871 | Displays | CR2.6

Thermal Infrared Imaging of Sea Ice During the MOSAiC Expedition

Linda Thielke, Gunnar Spreen, and Marcus Huntemann

How to cite: Thielke, L., Spreen, G., and Huntemann, M.: Thermal Infrared Imaging of Sea Ice During the MOSAiC Expedition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4871, https://doi.org/10.5194/egusphere-egu2020-4871, 2020.

EGU2020-5928 | Displays | CR2.6

Mapping Antarctic Grounding Lines from ICESat-2 Laser Altimetry

Tian Li, Geoffrey Dawson, Stephen Chuter, and Jonathan Bamber

The grounding line is the point where the grounded ice sheet detaches from the bed and begins to float. Knowledge of its position and dynamics are critical in mass budget assessments, ice sheet instability monitoring and ice sheet numerical modelling. The grounding line is typically mapped from the landward limit of tidal flexural using different satellite techniques, such as differential synthetic aperture radar interferometry (DInSAR) and ICESat-1 laser altimetry repeat track analysis. However, these methods have, to date, been limited by either spatial or temporal coverage. Launched on 15 September 2018, ICESat-2 satellite offers the potential to address both spatial and temporal coverage issues. Its six-beam pattern as well as the small footprint (~17 m in diameter) and high pulse repetition frequency (10 KHz) of laser altimeter instrument, can achieve a higher accuracy and an order of magnitude denser spatial coverage than ICESat-1. Here we present the results of mapping the grounding line position in Antarctica by detecting the landward limit of tidal flexure from a combination of ICESat-2 repeat track data with a crossover analysis of ascending and descending tracks. Grounding line positions mapped from this method are compared with previous estimates from DInSAR, ICESat-1 altimetry and the break-in-slope mapped from optical imagery. The results show an overall good agreement and highlight the improvements with the new satellite to provide high accuracy and density observations of grounding line in both space and time. 

How to cite: Li, T., Dawson, G., Chuter, S., and Bamber, J.: Mapping Antarctic Grounding Lines from ICESat-2 Laser Altimetry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5928, https://doi.org/10.5194/egusphere-egu2020-5928, 2020.

EGU2020-9411 | Displays | CR2.6

MODIS images anda avalanche: operational use of satellite images in forecasting avalanche Hazard .

Mauro Valt, Rosamaria Salvatori, and Roberto Salzano

The avalanche hazard is a critical task for the regional services in the Alpine region. For this reason, the characteristics of surface snow are continuously monitored in terms of micro-physics and metamorphism. The spatial distribution of the different types of snow covers (fresh snow, drift snow, melted snow, surface hoar, rain crusts, wet snow, dry snow) are used in the models aimed to forecast the avalanche hazard.

Satellite data are very important for routinely monitoring the snow cover and data provided by the Moderate Resolution Imaging Spectroradiometer (MODIS), onboard on the Terra and Aqua platforms, are an useful source of information for a modern avalanche assessment service.

More than one hundred MODIS images were processed, in the 2013-2020 period, for 2 areas located in the Dolomites, between Marmolada and Pale di San Martino groups (Veneto Region, Italy). The two training sites were used for the definition of a workflow useful for discriminating different types of snow surface. The defined workflow, based on the average radiometric values of bands 4, 5 and 6, were applied on the reflectances derived by the daily product MOD02HKM, with a spatial resolution of 500m. While band 4 and 5 (respectively visible radiation at 550nm and short-wave infrared at 1240nm) support the discrimination of different snow surfaces, the band 6 (short-wave infrared at 1630nm) is linked mainly to the presence of dry or wet snow on the surface.

The proposed workflow provided classification maps that were validated using observations recorded at the meteorological stations located in the test areas and by field surveys carried out by snow scientists. These results support the availability of a reliable tool based on remotely-sensed data, evidenced by the good agreement with field observations, which can be an optimal input for avalanche forecasting.

How to cite: Valt, M., Salvatori, R., and Salzano, R.: MODIS images anda avalanche: operational use of satellite images in forecasting avalanche Hazard ., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9411, https://doi.org/10.5194/egusphere-egu2020-9411, 2020.

EGU2020-9655 | Displays | CR2.6

CryoSat SIRAL: calibration and achievable performance after ten years of operations

Michele Scagliola, Marco Fornari, Marco Meloni, Jerome Bouffard, and Tommaso Parrinello

The main payload of CryoSat is a Ku-band pulsewidth limited radar altimeter, called SIRAL (Synthetic interferometric radar altimeter), that is equipped with two antennas for single-pass interferometric capability.

Due to the unique characteristics of SIRAL, a proper calibration approach was developed. In fact, not only corrections for transfer function, gain and instrument path delay have to be computed (as in previous altimeters), but also corrections for phase (SAR/SARIn) and phase difference between the two receiving chains (SARIN only). To summarize, SIRAL performs regularly four types of internal calibrations:

-           CAL1 in order to calibrate the internal path delay and long-term power drift.

-           CAL2 in order to compensate for the instrument IF transfer function.

-           CAL4 to calibrate the interferometer.

-           AutoCal, a specific sequence used to calibrate the gain and phase difference for each AGC setting.

After about 10 years of operational activity of the CryoSat satellite, the performance of the SIRAL instrument are revealed to be in line or better than the expected one.

In fact the calibration products, that have been designed to model a wide range of imperfections of the instrument, can be analyzed to highlight whether and how the instrument is changing over the time also as function of its thermal status. It is worth underlining here that each variation of the instrument measured by the calibration data is compensated in the Level1 processing. Inspecting the temporal evolution of the calibration data, SIRAL has been verified to be stable during its life. The performance of the SIRAL will be presented together with the outcomes of the stability analysis on the calibration data, in order to verify that the instrument has reached the requirements and that it is maintaining the performance over its life.

 

In order to monitor the performance of the CryoSat interferometer along the mission, in orbit calibration campaigns have been periodically performed about once a year. The end-to-end calibration strategy for the CryoSat interferometer uses the ocean surface as the known external target. In fact, the interferometer can be used to determine the across-track slope of the overflown surface and the slope of the ocean surface can be considered as known starting from the geoid. Denoting by β the across-track slope of the ocean and assuming that the knowledge error of the geoid slope is negligibly small, β can be compared with the across-track slope derived from CryoSat SARin Level1b products which results in β'=η(θ-χ) where η is a geometric factor, θ is the angle of earliest arrival measured by the CryoSat interferometer and χ is the baseline roll angle. By comparison of the expected across-track slope β and the measured across-track slope β', the accuracy and the precision of the angle of arrival θ measured by the CryoSat interferometer can be assessed.

In our analysis, the long-term accuracy (i.e. the closeness of the measurement to the true value) and the long-term precision (i.e. the closeness of agreement among a set of measurements) of the CryoSat interferometer have been assessed.

How to cite: Scagliola, M., Fornari, M., Meloni, M., Bouffard, J., and Parrinello, T.: CryoSat SIRAL: calibration and achievable performance after ten years of operations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9655, https://doi.org/10.5194/egusphere-egu2020-9655, 2020.

EGU2020-11405 | Displays | CR2.6

The NASA Operation IceBridge Sea Ice Freeboard, Snow Depth and Thickness Product

Jeremy Harbeck, Nathan Kurtz, and Alek Petty

Over the eleven-year lifetime of NASA’s Operation IceBridge, the Project Science Office has released an along-track sea ice freeboard, snow depth and thickness product in varying forms. Multiple versions of archival products are available for a number of the project’s early years and more recently quicklook versions, rapid-turnaround products primarily produced for summer sea ice forecasting, have been available for Arctic campaigns. During 2020, the mission’s close-out year, we are producing a final archival version of the product that will fill gaps in data availability and incorporate multiple improvements in the processing chain. These improvements include laser altimetry and snow radar pre-processing and ingestion upgrades, improved image analysis, updated tide and atmospheric models, updated gridding methodology and enhanced product outputs. The final result will constitute a state-of-the-art, internally self-consistent data product for all springtime Arctic and Antarctic Operation IceBridge campaigns.

How to cite: Harbeck, J., Kurtz, N., and Petty, A.: The NASA Operation IceBridge Sea Ice Freeboard, Snow Depth and Thickness Product, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11405, https://doi.org/10.5194/egusphere-egu2020-11405, 2020.

Glaciers in the southeastern part of the Tibet Plateau (TP) have experienced the most rapid mass loss over the High Mountain Asia. Hence, a multi-period investigation on the mass balance with focus on how glaciers evolve is imperative for better understanding of the glacier dynamics responding to climate change. Taking the Yanong glacier connected with a proglacial lake in the southeast TP as an example, we estimate the glacier mass budget at multiple-year and interannual timescales via reproducing a multiple-period DEM datasets, including KH-9 (1975), SRTM (2000), TanDEM-X (20112014) and SPOT-7 (2015) DEMs. We also estimate the penetration depths of both X- and C-band radar using Pléiades stereo images and TanDEM-X data , which are found to be 3.2 m and 4.5 m on average in this area. The results show that the Yanong glacier has been subject to an accelerated mass loss over the past four decades (19752015), and the tendency of surface thinning spread from low altitudes to high altitudes. Specifically, the mass balance of the Yanong glacier changes from 0.50 ± 0.13 m w.e./a (19742000) to 0.95 ± 0.13 m w.e./a (20002012) and to 1.02 ± 0.31 m w.e./a (20122015) at the multi-year timescale. A serious surface subsidence event is noted in areas that are about 2 km away from the glacier fronts after 2012, which are possibly caused by the internal/basal melting or collapsing. After further analyzing the evolution process of the proglacial lake, we found that the continuous disintegration of the glacier fronts may be the main reason for the accelerated mass deficit.

 

How to cite: Zhou, Y., Li, Z., Li, X., and Zheng, D.: Estimation of multi-period glacier mass balance in southeast Tibet using high-resolution remote sensing observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12890, https://doi.org/10.5194/egusphere-egu2020-12890, 2020.

EGU2020-15264 | Displays | CR2.6

The importance of slope correction for studying Greenland ice change using radar altimetry (CryoSat-2)

Katarzyna Sejan, Bert Wouters, and Michiel van den Broeke

Satellite radar altimetry is one of the most important tools for monitoring changes in the mass balance of the world's ice sheets. Acquiring long time series of elevation changes is crucial, and the long lifetime of the CryoSat-2 mission has contributed wonderfully to this effort. However, once the CryoSat-2 mission ends, it will be important to bridge the gap between CryoSat-2 and future radar altimetry missions. IceSat2 data can help aid this effort, assuming that the appropriate processing techniques are used to allow the comparison of radar and laser altimetry. Furthermore, different altimetry techniques come with their own pitfalls, in radar altimetry signal penetration into the snowpack introduces ambiguity in the origin of reflected echo, a major issue not present in laser altimetry. It is therefore important to minimize this ambiguity by developing processing algorithms for the radar altimetry form CryoSat-2 mission, with a special attention on relating it to the IceSat2 mission.  

Focusing on Greenland Ice Sheet (GIS), we have developed a processing chain for the estimation of surface elevations and elevation changes from the ESA level-1 product (L1b) Baseline D. As a first step, we investigated the importance of Digital Elevation Model (DEM) in the slope correction algorithm and how it affects the estimated surface elevation.

 

The waveform retracker algorithm was developed following the method by Nilsson (2015) with a range of thresholds in the threshold retracker applied to the waveform. Knowing the estimated range and the altitude of the satellite at the time of the measurement, we calculated the corresponding surface elevation at the point of the wavelet reflection.

We apply a slope correction method by Hurkmans (2012), where displacement from the nadir location in x- and y- directions is calculated using the slope angle and aspect retrieved from a DEM, giving a new set of coordinates that represents the location of the estimated elevation. We use two sets of slope angle and aspect calculated from two DEMs, ArcticDEM Release 7 (Porter et al., 2018) and Greenland Ice Mapping Project (GIMP) DEM (Howat et al., 2017). Both DEMs are similar in terms of optical imagery data source, processing and resolution, however, they have been referenced to different laser altimetry data. We investigate this effect in the slope correction of radar altimetry from CryoSat2 mission.

We checked the two sets of slope correction data using IceSat-2 data (Smith et al., 2019) corresponding to the same time period, and selected by nearest point calculation. We analyze and discuss the differences between IceSat-2 data and CryoSat-2 data with slope correction using GIMP DEM or ArcticDEM.

How to cite: Sejan, K., Wouters, B., and van den Broeke, M.: The importance of slope correction for studying Greenland ice change using radar altimetry (CryoSat-2), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15264, https://doi.org/10.5194/egusphere-egu2020-15264, 2020.

EGU2020-14036 | Displays | CR2.6

5 Years of Polar Land Ice Velocity and Discharge observed by Sentinel-1

Jan Wuite, Thomas Nagler, Markus Hetzenecker, Lars Keuris, Ludivine Libert, and Helmut Rott

Recent years have seen major advancements in satellite Earth observation of polar land ice. Among the most notable are the developments enabled by the Copernicus Sentinel program, including the Sentinel-1 SAR mission. The Sentinel-1 constellation, with its dedicated polar acquisition scheme, has provided the opportunity to derive ice flow velocity of the Greenland and Antarctic ice sheets at an unprecedented scale and temporal sampling. A continuous observational record of the ice sheet margins since October 2014, augmented by dedicated ice sheet wide mapping campaigns, enabled the operational monitoring of key climate variables like ice velocity and glacier discharge. In 2019 additional tracks have been added to the regular acquisition scheme, covering the slow-moving interior of the Greenland Ice Sheet, opening up new opportunities for interferometric applications and permitting to derive monthly ice sheet wide velocity maps. 


Based on repeat pass Sentinel-1 SAR data, acquired in Interferometric Wide (IW) swath mode, we have generated a dense archive of ice velocity maps covering the polar regions and encompassing the entire mission duration, now spanning well over 5 years. Including the latest observational data, we present ice velocity maps of Greenland, Antarctica and other major ice caps, focusing on time series of ice flow fluctuations of major outlet glaciers. The ice velocity maps, complemented by high resolution DEMs and ice thickness data, form the basis for studying ice dynamics and discharge fluctuations and trends at sub-monthly to multi-annual time scales. Our results underscore the value of long-term comprehensive monitoring of the polar ice masses, which is vital for to gain insight for predicting their response to ongoing climate warming.

This poster highlights some of the main achievements and latest developments of 5 years of Sentinel-1 ice flow mapping in the Polar regions facilitated by the ESA Climate Change Initiative (CCI), EU Copernicus Climate Change Service (C3S) and Austrian Space Applications Programme (ASAP). 

How to cite: Wuite, J., Nagler, T., Hetzenecker, M., Keuris, L., Libert, L., and Rott, H.: 5 Years of Polar Land Ice Velocity and Discharge observed by Sentinel-1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14036, https://doi.org/10.5194/egusphere-egu2020-14036, 2020.

EGU2020-18221 | Displays | CR2.6

Corner Reflectors for Validation of Ice Flow Velocity Derived from SAR Images along the CHINARE-Route in Antarctica

Gang Qiao, Rongxing Li, Tong Hao, Xiaohua Tong, Yanjun Li, Hongwei Li, Shuang Liu, Shijie Liu, Yuansheng Li, and Yinke Dou

Ice flow velocity is an important parameter for evaluating the stability of Antarctic ice shelves and analyzing the mass balance of the ice sheet. Large scale ice flow maps can be produced from satellite images with ground control and validation. Among various ground targets, corner reflectors show distinct intensity characteristics on SAR images due to its highly reflective surface shape and have been used for calibration and validation. This paper focuses on design and implementation of a set of corner reflectors to obtain the first-hand data of in-situ ice flow velocity for SAR image based ice velocity maps. The results should further help evaluate mass balance changes in East Antarctica using the input-output method.

Generally, the remote sensing method uses airborne or satellite optical and radar images from multiple periods to map ice flow velocity fields. The ground truth data are often sparse due to the harsh environment in the polar region. The annual Chinese Antarctic Research Expedition (CHINARE) makes it possible to obtain period field data of ice velocity within its campaign regions. The ~1200 km CHINARE-Route runs from Zhongshan Station to Kunlun Station along which the ice flow velocity varies from a few meters per year to 100s meters per year. 5 corner reflectors have been designed and installed along the 31st CHINARE-Route in 2015 and the 35th CHINARE-Route in 2019 (M1, M2 and M3 in the 31st CHINARE, A1and A2 in the 35th CHINARE). The ice flow velocities at the installation locations are of different orders of magnitude, about 44 m per year at the locations of M1 and A1, 93 m per year at M2 and M3 and 73 m per year at A2. The satellite orbit inclination, incident angle and the installation location were used to calculate the azimuth and elevation angles of the corner reflectors for installation. At all reflector locations GPS positions were collected at the time of installation. After that, the second time GPS coordinates of M3 in the 34th CHINARE in 2018, the third time GPS coordinates of M3, the second time GPS coordinates of A1 and A2 in the 36th CHINARE at the end of 2019 were measured respectively. TerraSAR-X was used to image the reflectors.

The results show that the mean in-situ ice flow velocity of M3 is 96.83 m per year between Feb. 2015 and Dec. 2019, with 97.51 m per year between Feb. 2015 and Jan. 2018 and 95.81m per year between Jan. 2018 and Dec. 2019. The in-situ ice flow velocity is 54.9 m per year at A1 between Jan. 2019 and Dec. 2019 and 86.92 m per year at A2 between Feb. 2019 and Dec. 2019. More TerraSAR-X and COSMO-SkyMed data will be used to extract the ice velocity corresponding to GPS measurements. The detailed information will be presented at the meeting.

How to cite: Qiao, G., Li, R., Hao, T., Tong, X., Li, Y., Li, H., Liu, S., Liu, S., Li, Y., and Dou, Y.: Corner Reflectors for Validation of Ice Flow Velocity Derived from SAR Images along the CHINARE-Route in Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18221, https://doi.org/10.5194/egusphere-egu2020-18221, 2020.

EGU2020-12619 | Displays | CR2.6

Cryospheric Applications of Novel GNSS Grazing Angle Reflections Collected by Spire CubeSats

Vu Nguyen, Takayuki Yuasa, Oleguer Nogués-Correig, Dallas Masters, Linus Tan, Timothy Duly, Robert Sikarin, Stephan Esterhuizen, Philip Jales, and Vahid Freemand

Spire Global operates the world’s largest and rapidly growing constellation of CubeSats performing GNSS based science and Earth observation. Currently, the Spire constellation, with many satellites in polar orbits, performs a variety of GNSS science, including radio occultation (GNSS-RO), ionosphere and space weather measurements, and precise orbit determination. These satellites have been primarily tasked to perform GNSS-RO to produce accurate profiles of atmospheric temperature, pressure, and water vapor and to collect millions of daily ionospheric total electron content measurements. Previous work showed that grazing angle reflections of GNSS signals off of ocean and sea ice surfaces serendipitously collected during radio occultation measurements had the potential to perform precision altimetry (< 10 cm) over sea ice surfaces.

In 2019, Spire reprogrammed its STRATOS GNSS science receiver to collect grazing angle reflection observations on Spire's large constellation of orbiting GNSS-RO satellites. To accomplish this, the open-loop tracking used in GNSS-RO collection was modified to perform open-loop prediction and tracking of grazing angle reflections between 5-30 deg elevation. Initial results confirm coherency of reflections over most sea ice surfaces and some open ocean surfaces. Full altimetric processing has been performed and is being productionized, confirming  sub-10 cm precision over sea ice where reflections were coherent, with some initial measurements showing altimetric height precision less than 2 cm RMS relative a mean sea surface (e.g., DTU18). Due to the large number of current and planned GNSS-RO satellites as Spire's constellation scales to over 100 operating GNSS-RO satellites, this technique has excellent potential to complement other sensors such as ICESat-2 and Cryosat-2.

A larger production period has now begun on multiple Spire satellites that will result in much larger quantities of diverse cryospheric measurements (sea ice as well as ice sheets will be sampled). We will present further results of this new and potentially revolutionary technique to use existing orbiting GNSS-RO satellite constellations to perform precision sea ice altimetry.

How to cite: Nguyen, V., Yuasa, T., Nogués-Correig, O., Masters, D., Tan, L., Duly, T., Sikarin, R., Esterhuizen, S., Jales, P., and Freemand, V.: Cryospheric Applications of Novel GNSS Grazing Angle Reflections Collected by Spire CubeSats, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12619, https://doi.org/10.5194/egusphere-egu2020-12619, 2020.

EGU2020-18542 | Displays | CR2.6

Climate parameters influencing satellite-based volume and elevation changes of the Antarctic ice sheet

Athul Kaitheri, Anthony Mémin, and Frédérique Rémy

Precisely quantifying the Antarctic Ice Sheet (AIS) mass balance remains a challenge as several processes compete at differing degrees in the basin-scale with regional variations. Understanding of changes in AIS has been largely based on observations from various altimetry missions and Gravity Recovery And Climate Experiment (GRACE) missions due to its scale and coverage. Analysis of linear trends in surface height variations of AIS since the early 1990s showed multiple variabilities in the rate of changes over the period of time. These observations are a reflection of various underlying ice sheet processes. Therefore understanding the processes that interact on the ice sheet is important to precisely determine the response of the ice sheet to a rapidly changing climate.

Changing climate constitutes variations in major short term processes including snow accumulation and surface melting. Variations in accumulation rate and temperature at the ice sheet surface cause changes in the firn compaction (FC) rate. Variations in the FC rate change the AIS thickness, that should be detected from altimetry, but do not change its mass, as observed by the GRACE mission. We focus our study on the seasonal and interannual changes in the elevation and mass of the AIS. We use surface elevation changes from Envisat data and gravity changes derived from the latest GRACE solutions between 10/2002 and 10/2010. As mass changes observed using the GRACE mission is strongly impacted by long term isostasy, as it involves mantle mass redistribution, we remove from all dataset an 8-year trend. We use weather variable historical data solutions including surface mass balance, temperature and wind velocities from the regional climate model RACMO2.3p2 as input to an FC model to estimate AIS elevation changes. We obtain a very good correlation between height change estimates from GRACE, Envisat and RACMO2.3p2 at several places such as along the coast of Dronning Maud Land, Wilkes land and Amundsen sea sector. Considerable differences in Oates and Mac Robertson regions, with a strong seasonal signal in Envisat estimates, reflect spatial variability in physical parameters of the surface of the AIS due to climate parameter changes such as winds.

How to cite: Kaitheri, A., Mémin, A., and Rémy, F.: Climate parameters influencing satellite-based volume and elevation changes of the Antarctic ice sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18542, https://doi.org/10.5194/egusphere-egu2020-18542, 2020.

EGU2020-18612 | Displays | CR2.6

Monitoring the Greenland Ice Sheet: A comparison between Sentinel-3 and CryoSat-2 radar altimeters

Jennifer Maddalena, Geoffrey Dawson, Stephen Chuter, Jack Landy, and Jonathan Bamber

Since 1992, satellite-borne radar altimetry has been used to record surface elevation change over the Greenland ice sheet (GrIS). Until the launch of CryoSat-2 in 2010, conventional radar altimeters performed poorly over high sloping terrain with heterogenous topography. The novel synthetic aperture radar interferometric (SARIn) mode of CryoSat-2 has improved capability in these regions over the margins of the GrIS, which have been experiencing the largest mass loss. ESA’s Sentinel-3 mission is the latest radar-altimeter to be launched. The first satellite, Sentinel-3A, was launched in February 2016 followed by Sentinel-3B April 2018. The Sentinel-3 satellites are the first to use synthetic aperture radar (SAR) across the interior of the GrIS. This has improved the along-track resolution to approximately 300m compared to CryoSat-2’s Low Resolution Mode (LRM) footprint which has a diameter of ~1.65km.

Here we assess the performance of Sentinel’s SAR mode compared to the LRM mode of CryoSat-2 over the interior of the ice sheet and the SARIn mode over the margins of the GrIS, through crossover analysis and a point-to-point comparison. We then assess the implications of this comparison for monitoring elevation changes over the ice sheet and we present rates of elevation change for June 2016 - June 2019 for both radar altimeter missions. To calculate rates of volume change from elevation change we use a statistical interpolation method, universal kriging, and present volume changes per basin over Greenland before comparing volume change estimates between CryoSat-2 and Sentinel-3.

How to cite: Maddalena, J., Dawson, G., Chuter, S., Landy, J., and Bamber, J.: Monitoring the Greenland Ice Sheet: A comparison between Sentinel-3 and CryoSat-2 radar altimeters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18612, https://doi.org/10.5194/egusphere-egu2020-18612, 2020.

EGU2020-20137 | Displays | CR2.6

Glacier calving front extraction from TanDEM-X DEM products of the Antarctic Peninsula

Yuting Dong, Lukas Krieger, Dana Floricioiu, and Ji Zhao

The Antarctic Peninsula (AP) is one of the most dynamic Polar regions and is experiencing fast mass loss. In order to quantify the mass changes of the AP and the associated sea level rise, an accurate estimate of its contemporary mass change is essential. The calving front location (CFL) is one important parameter to measure the geodetic mass balance or the dynamic mass loss of outlet glaciers. In order to quantify the mass change of Antarctic Peninsula glaciers on regional or individual glacier scales, the CFL with high spatial resolution is required. Because the Antarctic Peninsula has long, narrow coastlines, it is extremely time-consuming to delineate the detailed CFL from optical or SAR remote sensing images manually. Furthermore, it is also challenging for automatic algorithms to detect the whole glacier calving front line of AP considering the similarity of spectral and backscattering response of sea ice, grounded ice and mélange. Currently the most up-to-date coastal product covering the entire AP, which is provided by the Antarctic Digital Database (ADD), is manually delineated with all of the available remote sensing imagery acquired in various years. A frequently updated CFL product for the entire AP coastline is not available.

Therefore, we propose an efficient method to extract the current coastline of AP from bi-static TanDEM-X DEM products, including the 12 m TanDEM-X global DEM and newly processed RawDEMs with a precise time stamp.  The CFL between grounded ice or ice shelves and the ice mélange or open water is characterized by strong elevation gradients. Besides, the grounded ice and the ice shelf show smoother and more continuous elevation values in the TanDEM-X DEM while the ice mélange and open water are noisier. Hence the ice mélange at the CFL may look similar to grounded ice or ice shelves in optical and SAR images but can be distinguished in the TanDEM-X interferometric DEM. In our work, we combine elevation and elevation gradient information to separate grounded ice/ice shelves and ice mélange. Afterwards, terrain analysis and morphological operations are applied to remove the residual ice mélange pixels in the segmented image.

The TanDEM-X global DEM covering AP is a consistent, timely and high-precision DEM, which was generated from the bistatic InSAR data acquired by the TanDEM-X mission during austral winters 2013 and 2014. Thus our coastline of AP extracted from the 12 m TanDEM-X global DEM will correspond to the CFL of outlet glaciers of years 2013/2014. Furthermore, the CFL extracted from TanDEM-X RawDEMs with a particular time stamp can be used for geodetic mass balance calculation during different time periods. The extracted glacier calving front line reveals the potential of the high resolution height information in assisting the separation of grounded ice/ice shelf and ice mélange. The resulting glacier calving front line product of AP will be validated with the geocoded TanDEM-X backscattering amplitude images acquired at the date closest to the time stamp of the DEM tile and with the Antarctic coastline provided by the ADD.

How to cite: Dong, Y., Krieger, L., Floricioiu, D., and Zhao, J.: Glacier calving front extraction from TanDEM-X DEM products of the Antarctic Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20137, https://doi.org/10.5194/egusphere-egu2020-20137, 2020.

EGU2020-21748 | Displays | CR2.6

Quality Status of the CryoSat Data Products

Erica Webb, Ben Wright, Marco Meloni, Jerome Bouffard, Tommaso Parrinello, Steven Baker, David Brockley, Teresa Geminale, Michele Scagliola, and Marco Fornari

Launched in 2010, the European Space Agency’s (ESA) polar-orbiting CryoSat satellite was specifically designed to measure changes in the thickness of polar sea ice and the elevation of the ice sheets and mountain glaciers. Beyond the primary mission objectives, CryoSat is also valuable source of data for the oceanographic community and CryoSat’s sophisticated SAR Interferometric Radar Altimeter (SIRAL) can measure high-resolution geophysical parameters from the open ocean to the coast.

CryoSat data is processed operationally using two independent processing chains: Ice and Ocean. To ensure that the CryoSat products meet the highest data quality and performance standards, the CryoSat Instrument Processing Facilities (IPFs) are periodically updated. Processing algorithms are improved based on feedback and recommendations from Quality Control (QC) activities, Calibration and Validation campaigns, the CryoSat Expert Support Laboratory (ESL), and the Scientific Community. 

Since May 2019, the CryoSat ice products are generated with Baseline-D, which represented a major processor upgrade and implemented several improvements, including the optimisation of freeboard computation in SARIn mode, improvements to sea ice and land ice retracking and the migration from Earth Explorer Format (EEF) to Network Common Data Form (NetCDF). A reprocessing campaign is currently underway to reprocess the full mission dataset (July 2010 – May 2019) to Baseline-D.

The CryoSat ocean products are also generated in NetCDF, following a processor upgrade in November 2017 (Baseline-C). Improvements implemented in this new Baseline include the generation of ocean products for all data acquisition modes, therefore providing complete data coverage for ocean users. This upgrade also implemented innovative algorithms, refined existing ones and added new parameters and corrections to the products. Following the completion of a successful reprocessing campaign, Baseline-C ocean products are now available for the full mission dataset (July 2010 – present).

Since launch, the CryoSat ice and ocean products have been routinely monitored as part of QC activities by the ESA/ESRIN Sensor Performance, Products and Algorithms (SPPA) office with the support of the Quality Assurance for Earth Observation (QA4EO) service (formerly IDEAS+) led by Telespazio VEGA UK. The latest processor updates have brought significant improvements to the quality of CryoSat ice and ocean products, which in turn are expected to have a positive impact on the scientific exploitation of CryoSat measurements over all surface types.

This poster provides an overview of the CryoSat data quality status and the QC activities performed by the QA4EO consortium, including both operational and reprocessing QC. Also presented are the main evolutions and improvements that have implemented to the processors, and anticipated evolutions for the future.

How to cite: Webb, E., Wright, B., Meloni, M., Bouffard, J., Parrinello, T., Baker, S., Brockley, D., Geminale, T., Scagliola, M., and Fornari, M.: Quality Status of the CryoSat Data Products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21748, https://doi.org/10.5194/egusphere-egu2020-21748, 2020.

An accurate detection and mapping of glacial lakes in the Alpine regions such as the Himalayas, the Alps and the Andes are challenged by many factors. These factors include 1) a small size of glacial lakes, 2) cloud cover in optical satellite images, 3) cast shadows from mountains and clouds, 4) seasonal snow in satellite images, 5) varying degree of turbidity amongst glacial lakes, and 6) frozen glacial lake surface. In our study, we propose a fully automated approach, that overcomes most of the above mentioned challenges, to detect and map glacial lakes accurately using multi-source data and machine learning techniques such as the random forest classifier algorithm. The multi-source data are from the Sentinel-1 Synthetic Aperture Radar data (radar backscatter), the Sentinel-2 multispectral instrument data (NDWI), and the SRTM digital elevation model (slope). We use these data as inputs for the rule-based segmentation of potential glacial lakes, where decision rules are implemented from the expert system. The potential glacial lake polygons are then classified either as glacial lakes or non-glacial lakes by the trained and tested random forest classifier algorithm. The performance of the method was assessed in eight test sites located across the Alpine regions (e.g. the Boshula mountain range and Koshi basin in the Himalayas, the Tajiks Pamirs, the Swiss Alps and the Peruvian Andes) of the word. We show that the proposed method performs efficiently irrespective of geographic, geologic, climatic, and glacial lake conditions.

How to cite: Wangchuk, S. and Bolch, T.: Enhancing alpine glacial lakes detection and mapping using multi-source data and machine learning techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21811, https://doi.org/10.5194/egusphere-egu2020-21811, 2020.

EGU2020-2896 | Displays | CR2.6

Image Inpainting techniques for void filling in glaciological remote sensing products

Thorsten Seehaus, Bänsch Eberhard, McNabb Robert, and Braun Matthias

Remote sensing offers the possibility to efficiently monitor glacier changes on large scales and in remote regions. Glacier surface elevation changes and surface velocities can be derived automatically from satellite acquisitions and provide information on the evaluation of glacier dynamics and mass balance. However, the obtained data sets are often affected by voids due to various issues depending on the imaging technique (SAR, optical). Those missing data on the one hand lead to uncertainties in the quantification of glacier changes, on the other hand can limit the assimilation of the data sets in glacier models.

Inpainting techniques were developed to remove distortions from photographs or for retouch purposes. In this study, suitable Inpainting techniques are applied on glaciological remote sensing products and evaluated in comparison with previous attempts.

For Glacier Bay Alaska, a nearly complete coverage of a glacier area of ~6000 km² by surface elevation change information exists. Artificial voids were generated and filled by using different Inpainting techniques and parameter. The inpainted data sets are evaluated in comparison to the original data set.

How to cite: Seehaus, T., Eberhard, B., Robert, M., and Matthias, B.: Image Inpainting techniques for void filling in glaciological remote sensing products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2896, https://doi.org/10.5194/egusphere-egu2020-2896, 2020.

EGU2020-3280 | Displays | CR2.6

Automated mapping of Antarctic supraglacial lakes and streams using machine learning

Mariel Dirscherl, Andreas Dietz, Celia Baumhoer, Christof Kneisel, and Claudia Kuenzer

Antarctica stores ~91 % of the global ice mass making it the biggest potential contributor to global sea-level-rise. With increased surface air temperatures during austral summer as well as in consequence of global climate change, the ice sheet is subject to surface melting resulting in the formation of supraglacial lakes in local surface depressions. Supraglacial meltwater features may impact Antarctic ice dynamics and mass balance through three main processes. First of all, it may cause enhanced ice thinning thus a potentially negative Antarctic Surface Mass Balance (SMB). Second, the temporary injection of meltwater to the glacier bed may cause transient ice speed accelerations and increased ice discharge. The last mechanism involves a process called hydrofracturing i.e. meltwater-induced ice shelf collapse caused by the downward propagation of surface meltwater into crevasses or fractures, as observed along large coastal sections of the northern Antarctic Peninsula. Despite the known impact of supraglacial meltwater features on ice dynamics and mass balance, the Antarctic surface hydrological network remains largely understudied with an automated method for supraglacial lake and stream detection still missing. Spaceborne remote sensing and data of the Sentinel missions in particular provide an excellent basis for the monitoring of the Antarctic surface hydrological network at unprecedented spatial and temporal coverage.

In this study, we employ state-of-the-art machine learning for automated supraglacial lake and stream mapping on basis of optical Sentinel-2 satellite data. With more detail, we use a total of 72 Sentinel-2 acquisitions distributed across the Antarctic Ice Sheet together with topographic information to train and test the selected machine learning algorithm. In general, our machine learning workflow is designed to discriminate between surface water, ice/snow, rock and shadow being further supported by several automated post-processing steps. In order to ensure the algorithm’s transferability in space and time, the acquisitions used for training the machine learning model are chosen to cover the full circle of the 2019 melt season and the data selected for testing the algorithm span the 2017 and 2018 melt seasons. Supraglacial lake predictions are presented for several regions of interest on the East and West Antarctic Ice Sheet as well as along the Antarctic Peninsula and are validated against randomly sampled points in the underlying Sentinel-2 RGB images. To highlight the performance of our model, we specifically focus on the example of the Amery Ice Shelf in East Antarctica, where we applied our algorithm on Sentinel-2 data in order to present the temporal evolution of maximum lake extent during three consecutive melt seasons (2017, 2018 and 2019).

How to cite: Dirscherl, M., Dietz, A., Baumhoer, C., Kneisel, C., and Kuenzer, C.: Automated mapping of Antarctic supraglacial lakes and streams using machine learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3280, https://doi.org/10.5194/egusphere-egu2020-3280, 2020.

EGU2020-3643 | Displays | CR2.6

Temporal Multi-Looking of SAR Image Series for Glacier Velocity Determination and Speckle Reduction

Silvan Leinss, Shiyi Li, Philipp Bernhard, and Othmar Frey

The velocity of glaciers is commonly derived by offset tracking using pairwise cross correlation or feature matching of either optical or synthetic aperture radar (SAR) images.  SAR images, however, are inherently affected by noise-like radar speckle and require therefore much larger images patches for successful tracking compared to the patch size used with optical data. As a consequence, glacier velocity maps based on SAR offset tracking have a relatively low resolution compared to the nominal resolution of SAR sensors. Moreover, tracking may fail because small features on the glacier surface cannot be detected due to radar speckle. Although radar speckle can be reduced by applying spatial low-pass filters (e.g. 5x5 boxcar), the spatial smoothing reduces the image resolution roughly by an order of magnitude which strongly reduces the tracking precision. Furthermore, it blurs out small features on the glacier surface, and therefore tracking can also fail unless clear features like large crevasses are visible.

In order to create high resolution velocity maps from SAR images and to generate speckle-free radar images of glaciers, we present a new method that derives the glacier surface velocity field by correlating temporally averaged sub-stacks of a series of SAR images. The key feature of the method is to warp every pixel in each SAR image according to its temporally increasing offset with respect to a reference date. The offset is determined by the glacier velocity which is obtained by maximizing the cross-correlation between the averages of two sub-stacks. Currently, we need to assume that the surface velocity is constant during the acquisition period of the image series but this assumption can be relaxed to a certain extend.

As the method combines the information of multiple images, radar speckle are highly suppressed by temporal multi-looking, therefore the signal-to-noise ratio of the cross-correlation is significantly improved. We found that the method outperforms the pair-wise cross-correlation method for velocity estimation in terms of both the coverage and the resolution of the velocity field. At the same time, very high resolution radar images are obtained and reveal features that are otherwise hidden in radar speckle.

As the reference date, to which the sub-stacks are averaged, can be arbitrarily chosen a smooth flow animation of the glacier surface can be generated based on a limited number of SAR images. The presented method could build a basis for a new generation of tracking methods as the method is excellently suited to exploit the large number of emerging free and globally available high resolution SAR image time series.

How to cite: Leinss, S., Li, S., Bernhard, P., and Frey, O.: Temporal Multi-Looking of SAR Image Series for Glacier Velocity Determination and Speckle Reduction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3643, https://doi.org/10.5194/egusphere-egu2020-3643, 2020.

EGU2020-6739 | Displays | CR2.6

Assessment of a TanDEM-X Digital Elevation Model of the Greenland Ice Sheet and its Zonation for Winter 2015/16

Sabine Baumann, Birgit Wessel, Martin Huber, Silke Kerkhoff, and Achim Roth

The Greenland Ice Sheet (GIS) was the largest contributor to global sea level rise in the 2005 to 2016 period (Meredith et al. in press). Therefore, it is one of the biggest players influencing our climate and monitoring and understanding of its mechanisms and development are of highest relevance.

Means to observe and measure such large areas are remote sensing. The Tandem-X mission of DLR and Airbus consists of two satellites (TerraSAR-X and TanDEM-X) that are flying in single pass formation, mapping the Earth in interferometric SAR X-band with a resolution of 12m (Zink et al. 2014). The mission has been flying in this constellation since 2010. Due to the satellite constellation and the SAR system, digital elevation models (DEMs) can be created in high resolution, unaffected by the availability of daylight and the presence of clouds.

All data acquired between 2010 to 2014 (Rizzoli et al. 2017) were compled to a global elevation model. Besides this global product, several time slices were created for the GIS (Wohlfart et al. 2018). In this project, we created a DSM mosaic from winter 2015/16 acquisitions, more precisely using more than 2000 DEM scenes (Fritz at al. 2011) from end of October 2015 to beginning of February 2016.

One issue of a SAR system is the penetration of the signal into snow. Additionally, water surfaces appear dark in the images due to low backscatter towards the sensor. Therefore, we used winter scenes to minimize the height error.

We created an almost seamless DSM out of these scenes for 2015/16. Second, we used SAR features to delineate different snow zones. For this purpose, we used the amplitude, the height error map, and additionally ICESat and ICE Bridge data.

 

References
Fritz, T.; Rossi, C.; Yague-Martinez, N.; Rodriguez Gonzalez, F.; Lachaise, M.; Breit H. Interferometric processing of TanDEM-X data, IGARSS 2011, Vancouver, July 2011

Meredith, M.; Sommerkorn M.; Cassotta S.; Derksen C.; Ekaykin A.; Hollowed A.; Kofinas G.; Mackintosh A.; Melbourne-Thomas J.; Muelbert M.M.C.; Ottersen G.; Pritchard H.; and Schuur E.A.G.; 2019: Polar Regions. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.

Rizzoli, P.; Martone, M.; Gonzalez, C.; Wecklich, C.; Tridon, D.B.; Bräutigam, B.; Bachmann, M.; Schulze, D.; Fritz, T.; Huber, M.; et al. Generation and performance assessment of the global TanDEM-X digital elevation model. ISPRS J. Photogramm. Remote Sens. 2017, 132, 119–139.

Wohlfart, C.; Wessel, B.; Huber, M.; Leichtle, T.; Abdullahi, S.; Kerkhoff, S.; Roth, A. TanDEM-X DEM derived elevation changes of the Greenland Ice Sheet. In Proceedings of the IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Valencia, Spain, 22–27 July 2018.

Zink, M.; Bachmann, M.; Bräutigam, B.; Fritz, T.; Hajnsek, I.; Krieger, G.; Moreira, A.; Wessel, B. TanDEM-X: The New Global DEM Takes Shape. IEEE GRSM 2014, 2, 8–23.

How to cite: Baumann, S., Wessel, B., Huber, M., Kerkhoff, S., and Roth, A.: Assessment of a TanDEM-X Digital Elevation Model of the Greenland Ice Sheet and its Zonation for Winter 2015/16, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6739, https://doi.org/10.5194/egusphere-egu2020-6739, 2020.

Abstract: The iceberg freeboard is an important geometric parameter for measuring the thickness of the iceberg and then estimating its volume. Based on the fact that the iceberg can cast elongated shadow on the surface of sea ice in winter, this paper proposes a method to measure the iceberg freeboard using shadow length and the predefined or estimated solar elevation angle. Three Landsat-8 panchromatic images are selected to test our method, with center solar elevation angle of respectively 5.43°, 7.49°and 11.01° on August 29, September 7, and 16 September in 2016. Shadow lengths of five isolated tabular icebergs are automatically extracted to calculate the freeboard height. For the accuracy assessment, we use the matching points at the different time as cross validation. The results show that the measurement error of shadow length is less than one pixel. When the sun elevation angle is lower than 11.01°, the Root Mean Square Error (RMSE) of the iceberg freeboard from the panchromatic 15 m image is less than 2.0 m, and the Mean Absolute Error (MAE) is less than 1.5 m. Such experiment shows that: under the angle of low solar elevation in winter, the landsat-8 panchromatic 15 m image can be used for high-precision measurement of the iceberg freeboard, and has the potential to measure the Antarctic iceberg freeboard in large scale.

Key words: Antarctic, icebergs, freeboard, shadow altimetry, Landsat-8

 

How to cite: Guan, Z. and Liu, Y.: Extracting icebergs freeboard from the shadows in Landsat-8 panchromatic images , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12810, https://doi.org/10.5194/egusphere-egu2020-12810, 2020.

EGU2020-16492 | Displays | CR2.6

Complex multi-decadal ice dynamical change within the interior of the Greenland Ice Sheet

Joshua Williams, Noel Gourmelen, and Peter Nienow

Observations of ice dynamical change in the interior of the Greenland Ice Sheet, at distances >~100 km from the ice-margin, are sparse, exhibiting very low spatial and temporal resolution (e.g. Sole et al., 2013; Doyle et al., 2014; Van de Wal et al., 2015). As such, the behaviour of interior Greenland ice represents a significant unknown in our understanding of the likely response of the ice sheet to oceanic and atmospheric forcing. The observation of a 2.2 % increase in ice velocity over a three-year period at a location 140 km from the ice margin in South West Greenland (Doyle et a., 2014) has been inferred to suggest that the ice sheet interior has undergone persistent flow acceleration. It remains unclear, however, whether this observation is representative of wider trends across the ice sheet.

Here, we investigate changes in ice motion within Greenland’s interior by utilising recent satellite-derived ice velocities covering the period 2013-2018 (Gardner et al., 2019) in conjunction with in-situ velocities collected at 30 km intervals along the 2000 m elevation contour during the mid-1990s (Thomas et al., 2000). Previous observations from the late-1990s/early-2000s through to late-2000s/early-2010s have revealed significant speed-up at many of Greenland’s tidewater glaciers (e.g. Bevan et al., 2012; Murray et al., 2015), in contrast to widespread deceleration within the ablation zone of the South West land-terminating margin (e.g. Tedstone et al., 2015; Van de Wal et al., 2015; Stevens et al., 2016). The recent availability of satellite data enables us to compare annual ice velocities from the period 2013-2018 to those collected at GPS stations in the mid-1990s, thereby enabling us to detect any long-term changes in ice-sheet wide inland ice motion during a period of considerable climatic and potentially significant dynamic change.

We observe multi-decadal interior ice acceleration of >15 % at Jakobshavn Isbrae, with similar inland accelerations at Kangerlugssuaq, Sermiligarssuk Brae and Narsap Sermia, and smaller velocity increases upstream of other marine-terminating outlets; these accelerations suggest that dynamic change at the margins has propagated considerable distances into the ice sheet interior. By contrast, ice velocities have slowed inland of some tidewater outlets such as Helheim Glacier, Umiamako Isbrae and Hagen Brae, confirming complex spatial variability in interior response to oceanic and atmospheric forcing. Furthermore, whilst prior work suggested that South West Greenland’s land-terminating sector experienced persistent interior speed-up between 2009 and 2012 (Doyle et al., 2014), our results reveal a >10% multi-decadal slowdown within the same sector, suggesting this region is resilient to recent increases in surface melt forcing.

How to cite: Williams, J., Gourmelen, N., and Nienow, P.: Complex multi-decadal ice dynamical change within the interior of the Greenland Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16492, https://doi.org/10.5194/egusphere-egu2020-16492, 2020.

EGU2020-17311 | Displays | CR2.6

Mapping Arctic Sea Ice Surface Roughness with Multi-angle Imaging SpectroRadiometry

Thomas Johnson, Michel Tsamados, Jan-Peter Muller, and Julienne Stroeve

Surface roughness is a crucial parameter in climate and oceanographic studies, constraining momentum transfer between the atmosphere and ocean, providing preconditioning for summer melt pond extent, while also closely related to ice age. High resolution roughness estimates from airborne laser measurements are limited in spatial and temporal coverage while pan-Arctic satellite roughness have remained elusive and do not extended over multi-decadal time-scales.  The MISR (Multi-angle Imaging SpectroRadiometer) instrument acquires optical imagery at 275m (red channel) and 1.1 km (all channels) resolutions from nine near-simultaneous camera view zenith angles sampling specular anisotropy, since 1999. Extending on previous work to model sea ice surface roughness from MISR angular reflectance signatures, a training dataset of cloud-free pixels and coincident probability distribution functions of lidar derived elevations from the Airborne Topographic Mapper (ATM) is generated. Surface roughness, defined as the standard deviation of the within-pixel elevations to a best-fit plane, is modelled using Support Vector Regression with a Radial Basis Function kernel, hyperparameters are tuned using GridSearchCV, and performance is assessed using nested cross-validation. We present derived instantaneous and monthly averaged sea ice roughness products at 1.1km and 17.6km resolution over the timespan of IceBridge campaigns (March and April for 2009-2018) on an EASE-2 (Equal-Area Scalable Earth) grid. These show considerable promise in detecting newly formed smooth ice from polynyas, and detailed surface features such as ridges and leads.

 

How to cite: Johnson, T., Tsamados, M., Muller, J.-P., and Stroeve, J.: Mapping Arctic Sea Ice Surface Roughness with Multi-angle Imaging SpectroRadiometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17311, https://doi.org/10.5194/egusphere-egu2020-17311, 2020.

EGU2020-18866 | Displays | CR2.6

Mapping Antarctic sea ice albedo properties from MISR fused with MODIS

Jan-Peter Muller and Said Kharbouche

In [1] a new method is described for fusing spectral BRF and derived albedo at 1.1km within the 7 minutes that MISR acquires images of a surface point with coincident MODIS nadir spectral data processed into a 1km sea ice mask. NetCDF products were produced in polar stereographic projection and produced on daily, weekly, fortnightly and monthly from November to February each year from 2000-2016. Arctic sea ice albedo has been previously presented and in this presentation, Antarctic time series, will be presented covering the same time period. This area has less complete coverage than the Arctic due to data outages due to telecommunications issues. [2] has recently pointed out that sea ice coverage  has  reduced dramatically since 2014, mainly one quadrant centred on the Wendell sea and the spectral albedo for this area will be highlighted.

Acknowledgements: Support was provided by EU-FP7 QA4ECV (Quality Assurance for Essential Climate Variables) under Project Number 607405 for the development of the processing system.

References:
[1] Kharbouche, S.; Muller, J.-P. Sea Ice Albedo from MISR and MODIS: Production, Validation, and Trend Analysis. Remote Sens. 2019, 11, 9. doi: https://doi.org/10.3390/rs11010009

[2] Parkinson, C. A 40-y record reveals gradual Antarctic sea ice increases followed by decreases at rates far exceeding the rates seen in the Arctic. Proceedings of the National Academy of Sciences. 2019, 116 (29) 14414-14423; DOI: 10.1073/pnas.1906556116

How to cite: Muller, J.-P. and Kharbouche, S.: Mapping Antarctic sea ice albedo properties from MISR fused with MODIS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18866, https://doi.org/10.5194/egusphere-egu2020-18866, 2020.

EGU2020-20124 | Displays | CR2.6

Listening to glaciers in Greenland

Läslo G. Evers, Pieter S.M. Smets, Shahar Shani-Kadmiel, and Jelle D. Assink

Inaudible sound, i.e., infrasound, from glaciers is generated by glacier run-off and during calving events. Such sounds can be continuously monitored with microbarometer arrays. Changes in the rate of events can be retrieved with a resolution of a few seconds. Applying array processing techniques enables the identification of individual glaciers over ranges of tens of kilometers. We concentrated on the remote region around Qaanaaq in northwestern Greenland and found coherent infrasound of at least five glaciers over a period of 16 years. Knowledge on the dynamical behavior of these remote glaciers, and other glaciers, is important for assessing hazards due to glacier melt and calving, mass balance of ice sheets and consequently sea level rise. Here we use a novel technique involving passive infrasound measurements to show that remote land and sea terminating glaciers behave differently in terms of their temporal behavior during the seasons and years. Strong fluctuations in infrasonic activity are found over time, with the highest activity rates in 2019. Increased activity over the years of the land- ans sea-terminated glaciers is retrieved. We anticipate that monitoring glacier infrasound can contribute to complementary knowledge of the behavior of remote glaciers, as the glacial dynamics can be passively observed on a fine temporal scale.

How to cite: Evers, L. G., Smets, P. S. M., Shani-Kadmiel, S., and Assink, J. D.: Listening to glaciers in Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20124, https://doi.org/10.5194/egusphere-egu2020-20124, 2020.

EGU2020-20949 | Displays | CR2.6

Antarctic ice and snow surface temperature retrieval from MODIS and Landsat8

Tingting Liu, Yachao Li, Zemin Wang, Weifeng Hao, Songtao Ai, and Chunxia Zhou

Ice surface temperature (IST) is of utmost importance to the ice sheet radiation budget and mass balance, which has been documented by many scientific researches.

This research firstly proposes an effective approach to retrieve IST in the Antarctic area by presenting a modified split-window algorithm (SWA) and introducing a polynomial fitting for atmospheric transmittance simulation. The effectiveness was quantitatively validated by a comparative study with a Moderate Resolution Imaging Spectroradiometer (MODIS) IST product (MOD29) and automatic weather station (AWS) data from Zhongshan Station and the Ross Ice Shelf from 2004 to 2013. From the algorithm validation and data comparison, it was found that: 1) The polynomial fitting can better describe the relationship between water vapor and atmospheric transmittance, with higher determination coefficients (0.99887 for band 31 and 0.99895 for band 32, respectively) and lower residual sum of squares (0.000373 for band 31 and 0.000234 for band 32, respectively). 2) Using the Zhongshan Station data set, the retrieved ISTs by the proposed method were more accurate than the MOD29 product, with a bias of −0.61 K and a root-mean-square error (RMSE) of 1.32 K; comparatively, the bias for MOD29 was −1.33 K and the RMSE for MOD29 was 1.81 K. 3) The proposed method also obtained the highest accuracy in the other experiment using the Ross Ice Shelf data set, in which the bias and RMSE for the retrieved ISTs were −1.62 K and 2.34 K, respectively; the corresponding accuracies for MOD29 were −2.54 K and 3.04 K, respectively. Overall, it was found that the proposed method shows a robust performance in Antarctic IST retrieval for MODIS data.

Besides, an improved single-channel (SC) algorithm is proposed for retrieving the ice surface temperature of polar regions from Landsat8 band10 in this study. The improved algorithm avoids using Taylor's theorem and eliminates Taylor approximation error. In addition, the atmospheric parameters suitable for polar regions are simulated and the effective mean atmospheric temperature is added to the fitting process. In order to maintain the advantage of the SC algorithm minimum input data requirements, the effective mean atmospheric temperature is obtained by using the existing parameters and iterative calculation. The results of sensitivity analysis show that the improved algorithm is not sensitive to atmospheric water vapor content but sensitive to the calibration precision of thermal infrared sensor. Theoretical verification results show that the RMSEs of the SC algorithm and the improved SC algorithm are 0.72 K and 0.33 K, respectively. Compared with MODIS land surface temperature product, the RMSE of the improved SC algorithm is 0.31K. Compared with the temperature of automatic weather stations, in the Antarctic, the RMSE of SC algorithm is of 1.48 K and the improved SC algorithm is 1.22 K. In conclusion, the improved SC algorithm performs better than SC algorithm in polar ice surface temperature retrieval.

How to cite: Liu, T., Li, Y., Wang, Z., Hao, W., Ai, S., and Zhou, C.: Antarctic ice and snow surface temperature retrieval from MODIS and Landsat8, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20949, https://doi.org/10.5194/egusphere-egu2020-20949, 2020.

CR2.7 – Glacier Monitoring from In-situ and Remotely Sensed Observations

EGU2020-5135 | Displays | CR2.7

Glacier monitoring, capacity building and related cryospheric research in Central Asia

Martin Hoelzle, Martina Barandun, Tomas Saks, Erlan Azisov, Abror Gafurov, Alyssa Ghirlanda, Abdulhamid Kayumov, Ruslan Kenzhebaev, Marlene Kronenberg, Horst Machguth, Halim Mamirov, Bolot Moldobekov, Maxim Petrov, Nadine Salzmann, Ryskul Usubaliev, Andrey Yakovlev, and Michael Zemp

Climate change is a major challenge for humanity and the related global implications will influence and threaten future economies and livelihood of coming generations, especially in developing countries. Central Asia is one of the regions mostly vulnerable to climate change considering its hydrological constraints. Tien Shan and Pamir, are among the largest mountain systems of the world, and play a significant role in serving water to the arid and continental region. Future water resources in Central Asia depend strongly on the cryosphere, particularly on snow, glaciers and permafrost. These cryospheric components store enormous amounts of fresh water and under the ongoing climate warming, expected changes will play an important role for future water availability in the region. Recent research clearly points out that a) for current climate conditions, water release by the cryosphere, particularly glaciers, is fundamental to keep runoff sufficient during the dry summer months and b) at the end of this century the water contribution of glaciers will be drastically reduced. Certain catchments are expected to completely dry-out. This setting creates a complex set of future challenges in the domains of water management, energy production, irrigation, agriculture, environment, disaster risk reduction, security and public health and potential political tension and conflicts between the countries cannot be excluded.

Notably, climate change also poses challenges in the field of climate services, as the lack of reliable data and commitment of the governments to fully integrate their observatory systems inhibits the sustainable adaptation and development of the region. At this point, the project CICADA (Cryospheric Climate Services for improved Adaptations) is currently contributing to the improvement of the Cryospheric Climate Services in the Central Asian countries by installing modern monitoring infrastructure, by training local students and researchers and by using the collected in situ measurements in combination with remote sensing and modelling to provide climate scenarios and services for water runoff and natural hazards. This is a prerequisite to allow early planning and adaptation measures within the water resource management and disaster risk reduction sectors.

How to cite: Hoelzle, M., Barandun, M., Saks, T., Azisov, E., Gafurov, A., Ghirlanda, A., Kayumov, A., Kenzhebaev, R., Kronenberg, M., Machguth, H., Mamirov, H., Moldobekov, B., Petrov, M., Salzmann, N., Usubaliev, R., Yakovlev, A., and Zemp, M.: Glacier monitoring, capacity building and related cryospheric research in Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5135, https://doi.org/10.5194/egusphere-egu2020-5135, 2020.

EGU2020-11382 | Displays | CR2.7 | Highlight

Manifestations and mechanisms of the Karakoram glacier Anomaly

Daniel Farinotti, Walter W. Immerzeel, Remco J. de Kok, Duncan J. Quincey, and Amaury Dehecq

Due to ongoing climatic change, glacier mass loss and retreat are observed all over the globe. The changes are beyond historic precedence, affect ice masses from the polar ice sheets to the highest mountain glaciers, and cause concerns ranging from rising sea levels to water scarcity. The impacts on water resources are particularly important when glaciers supply water to downstream populations, as is the case in High Mountain Asia (HMA).

Amongst this general picture of glacier wastage, one region stands out because of its anomalous behavior: The Karakoram. Located in the border regions of China, India, and Pakistan, the Karakoram and the nearby Western Kun Lun have been identified as a region in which glaciers were in balance or even slightly gaining mass during recent decades. Geodetic assessments show negligible to slightly positive volume changes, analyses of surface ice flow velocities show steady to increasing ice flow, and glacier inventories reveal a concentration of surge-type glaciers that is unique to HMA.

In this contribution, we review the present-day understanding of what has been known as the “Karakoram Anomaly” since the early 2000s. We show that evidence is accumulating for the Anomaly extending into the Western Kun Lun and Pamirs, and for being due to a combination of factors, including (i) an increase in westerlies-dominated winter snowfalls, (ii) an increase in diurnal temperature ranges possibly related to large-scale deforestation, (iii) a summer cooling linked to the weakening of the monsoon, (iv) an increase in atmospheric moisture likely due to an expansion of  regional irrigation, (v) an increase in summer accumulation resulting from both the summer cooling and the increased moisture, and (vi) reduced ablation due to a moisture-related increase in cloudiness and decrease in incoming shortwave radiation.

Our work assesses the relative level of confidence of the individual mechanisms, and highlights potential pathways that may further improve our understanding.

How to cite: Farinotti, D., Immerzeel, W. W., de Kok, R. J., Quincey, D. J., and Dehecq, A.: Manifestations and mechanisms of the Karakoram glacier Anomaly, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11382, https://doi.org/10.5194/egusphere-egu2020-11382, 2020.

EGU2020-21221 | Displays | CR2.7

Forcings of mass-balance variability in Karakoram-Himalaya

Pankaj Kumar, Vladimir A. Ryabchenko, Aaquib Javed, Dmitry V. Sein, and Md. Farooq Azam

Glacier retreat is a key indicator of climate variability and change. Karakoram-Himalaya (KH) glaciers are the source of several perennial rivers protecting water security of a large fraction of the global population. The region is highly vulnerable to climate change impacts, hence the sensitivity of KH glaciers to regional microclimate, especially the impact of individual parameters forcing have been not quantified yet. The present study, using a coupled dynamical glacier-climate model simulation results, analyses the modelled interannual variability of mass-balance for the period 1989-2016. It is validated against available observations to quantify for the first time the sensitivity of the glaciers mass-balance to the individual forcing over KH. The snowfall variability emerges as the key factor, explaining ~60% of the variability of regional glacier mass balance. We provide insight into the recent divergent glacier response over the Karakoram Himalaya. The results underline the need for careful measurements and model representations of snowfall spatiotemporal variability, one of the HK's least-studied meteorological variables, to capture the large-scale, but region-specific, glacier changes at the third pole.

 

 

 

Acknowledgement:

The work was supported by Indian project no. DST/INT/RUS/RSF/P-33/G, and the Russian Science Foundation (Project 19-47-02015).

How to cite: Kumar, P., Ryabchenko, V. A., Javed, A., Sein, D. V., and Azam, Md. F.: Forcings of mass-balance variability in Karakoram-Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21221, https://doi.org/10.5194/egusphere-egu2020-21221, 2020.

EGU2020-15516 | Displays | CR2.7 | Highlight

Dynamics and drivers of High Mountain Asia’s glacier change from the mid 1980s to late 2019

David Loibl, Georgy Ayzel, Fiona Clubb, Inge Grünberg, and Jan Nitzbon

For only two out of more than 95 * 10³ glaciers in High Mountain Asia (HMA) a continuous time series of mass balance measurements covering more than 30 years (World Glacier Monitoring Service’s ‘reference glaciers’) is available to date. Considering that both glaciers are located in the Tian Shan Range, i.e. the northernmost part of HMA, and that glacier changes in HMA is known to be heterogeneous in space and time, it is clear that a substantial knowledge gap exists regarding the actual dynamics at individual glaciers and their forcing. 

Here, we present a novel data set of transient snowline altitude (TSLA) measurements covering all glaciers > 0.5 km² in HMA (n=28,501) for a time frame from the mid 1980s to late 2019 based on more than 10⁵ Landsat satellite images, allowing for investigations of the characteristics of glacier change at unprecedented spatio-temporal resolution and coverage.

Individual glacier’s total maxima of end-of-season TSLAs for the whole period of observation clearly highlight years with many (i.e. 1994, 2009, 2013, 2015) and few (i.e. 1995, 2003, 2012) maxima. Out of the glaciers that show a significant trend throughout the observation period, 90.8% have a positive trend with a median TSLA rise of 7.0 m/year. These figures increase to 95.8% and 13.8 m/year, when only observations of the last two decades are considered.

Based on ERA5 meteorological time series and fundamental physiographic glacier characteristics from the Randolph Glacier Inventory v6, we investigated drivers of the observed TSLA fluctuations. Consistent with expectations, a Random Forest analysis finds temperature to be the dominant meteorological driver of TSLA dynamics throughout all regions of HMA when whole years are considered. Conversely, meteorological forcing regimes are highly heterogeneous for different glaciers in the ablation phase, with wind, air temperature and incoming shortwave radiation being the dominant TSLA drivers for the majority of glaciers in HMA. Considering regional domains, TSLA dynamics are considerably determined by physiographic factors, such as latitude, longitude, hypsographic characteristics, slope and aspect of individual glaciers. A hierarchical clustering analysis shows distinct groups of similar forcing setups exist; Their spatial distribution, however, rather follows specific positions in the topoclimatic system than forming distinct regional clusters or aligning to large-scale gradients.

In summary, our findings indicate that spatial and temporal patterns of glacier change in HMA are considerably more complex than currently known. Multidecadal high-resolution TSLA datasets like the one presented here may inform future research to disentangle the complex topoclimatic process-response systems that control the adaptation of individual glaciers to climate change.

How to cite: Loibl, D., Ayzel, G., Clubb, F., Grünberg, I., and Nitzbon, J.: Dynamics and drivers of High Mountain Asia’s glacier change from the mid 1980s to late 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15516, https://doi.org/10.5194/egusphere-egu2020-15516, 2020.

EGU2020-17796 | Displays | CR2.7

Ice loss in Patagonia and Tierra del Fuego glaciers during the first two decades of the 21st century

David Farías, Philipp Malz, Thorsten Seehaus, Christian Sommer, Lukas Sochor, and Matthias Braun

Patagonian and Tierra del Fuego Glaciers are among the highest contributors to sea level rise in the Southern Hemisphere. Although this is an area gaining more attention through recent studies, continuous remotely sensed monitoring is only nascent, but crucial for a better understanding of the glacier changes in this region. Here, we present an update of the glacier elevation and mass changes of Patagonia and Tierra del Fuego glaciers, applying differential synthetic aperture radar (SAR) interferometry using data from the Shuttle Radar Topography Mission (SRTM) and the German TerraSAR-X-Add-on for Digital Elevation Measurements mission (TanDEM-X). Our study covers the period between 2000 and 2019. Here, we particularly estimated the glacier mass loss regionalized for the Northern and Southern Patagonia Icefield (NPI and SPI) and Tierra del Fuego, which includes the Icefields of Cordillera Darwin and Gran Campo Nevado.

Our preliminary results indicate mass loss rates of 4.75 ± 0.35 Gt a-1 for NPI for the period of 2000-2019. Results for both other regions will be also presented. Alongside an accuracy assessment based on GNSS field campaign data and satellite laser altimetry.  

How to cite: Farías, D., Malz, P., Seehaus, T., Sommer, C., Sochor, L., and Braun, M.: Ice loss in Patagonia and Tierra del Fuego glaciers during the first two decades of the 21st century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17796, https://doi.org/10.5194/egusphere-egu2020-17796, 2020.

EGU2020-13782 | Displays | CR2.7

Automatic glacier outlines extraction from Sentinel-1 and Sentinel-2 time series

Riccardo Barella, Mattia Callegari, Carlo Marin, Claudia Notarnicola, Marc Zebisch, Rudolf Sailer, Christoph Klug, Shtephan Galos, Roberto Dinale, and Stefano Benetton

Glaciers represent an important part of the hydrologic cycle in the Alps and they are very sensitive to climate change. Satellite remote sensing is an efficient tool for glacier monitoring because it provides a synoptic view over large areas. In literature, well-established methods for glacier delineation based on the Red and Short Wave Infrared (SWIR) ratio have been presented. These methods depend on a manual selection for each glacier of the “best scene”, i.e. absence of cloud coverage and minimum snow cover. A further manual refinement step is needed to handle possible errors, mainly due to cloud cover or shadows, and to include debris covered ice.

A manual approach for glacier outline extraction, especially if applied over large areas and beside the respective extraordinary amount of work, may be inadequate for at least two reasons:

1) The increased amount of available satellite data provided by the recently launched Sentinel-2 mission, which ensure at least one acquisition every 5 days on a given area;

2) The need for a more frequent update of the glacier outlines i.e. few years, due to the faster changes affecting glaciers during the last years.

In this work, we present an automatic method for glacier mapping, including bare ice and debris covered ice through the synergetic use of Sentinel-1 and Sentinel-2. The information of the Sentinel-2 time series is first classified with a Support Vector Machine (SVM) to detect cloud and snow. The snow and cloud masks are then used to select the non-cloudy pixels with the lowest snow coverage in the surrounding area. This is done by applying a moving window on the entire multi-temporal classified stack. The selected pixels for each band compose a multi-temporal cloud free mosaic, which represents the glaciers with the minimum snow cover for the current ablation season i.e., the “best scene”. If we compose the mosaic with classified pixels instead of the reflectance, we obtain the glacier – non glacier map that we use for outlines extraction. On the other hand, the Sentinel-1 coherence is used to detect the debris-covered ice over the areas classified as non-glacier from Sentinel-2. In detail, the Sentinel-1 time series is exploited to generate a multi-temporal coherence mosaic, which is representative of the loss of coherence due to the movement of the debris only. By properly thresholding this mosaic and considering the topographic information, the outlines of debris covered glaciers can be extracted.

The results obtained with the proposed method are compared with the recent official glacier inventory of South Tyrol (Italy) and Tyrol (Austria), which was derived from the manual interpretation of aerial orthophotos and lidar data by glacier experts.

How to cite: Barella, R., Callegari, M., Marin, C., Notarnicola, C., Zebisch, M., Sailer, R., Klug, C., Galos, S., Dinale, R., and Benetton, S.: Automatic glacier outlines extraction from Sentinel-1 and Sentinel-2 time series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13782, https://doi.org/10.5194/egusphere-egu2020-13782, 2020.

EGU2020-21056 | Displays | CR2.7

New Glacier Inventory of the Russian glaciers based on Sentinel images (2017/2018).

Tatiana Khromova, Gennady Nosenko, Andrey Glazovsky, Stanislav Nikitin, and Anton Muraviev

We present new Glacier Inventory of the Russian glaciers based on Sentinel images (2017/2018).

The modern reduction in the size of glaciers is accompanied by the activation of natural processes leading to catastrophic consequences, changes in landscapes and prevailing nature management practices. To reduce risks and adapt to the consequences of ongoing changes, relevant data on the state of glacial systems are needed. In Russia, extensive glaciation is present in the Arctic zone, and in its continental part there are 18 mountain-glacial systems. According to the Glacier Inventory of the USSR in the mid-twentieth century in Russia there were 7167 glaciers with a total area of ​​60103, 99 km2. Of these, 685 glaciers with an area of ​​56,127.2 km2 accounted for the Arctic archipelagos. Despite the ever-increasing amount of information from space, and experimental studies in a number of glacial regions, a complete and reliable picture of the state of glaciation in Russia at the beginning of the 21st century has not been available to date.
The project aims to develop and create a unified information basis for the study of glacial regions of Russia using geoinformation technologies. The initial data were collected and systematized to assess the current state of Russia's glaciers: data from previous inventories, maps, historical and modern aerial and space images, digital elevation models. A classification of possible catastrophic phenomena of glacial genesis was developed: dynamically unstable glaciers, glacier lakes, icebergs, etc. The structure of the database for the study of Russian glaciers is developed, compatible with world and national data archives. Implementation of the project allowed to gain new knowledge about the state of Russian glaciers.

The presentation includes the results obtained in the framework of the following research projects: № 0148-2019-0004 of the Research Plan of the Institute of Geography of the Russian Academy of Sciences, № 05/2019/RGS-RFBR supported by the Russian Geographical Society, № 18-05-60067  supported by RFBR.

How to cite: Khromova, T., Nosenko, G., Glazovsky, A., Nikitin, S., and Muraviev, A.: New Glacier Inventory of the Russian glaciers based on Sentinel images (2017/2018)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21056, https://doi.org/10.5194/egusphere-egu2020-21056, 2020.

EGU2020-3901 | Displays | CR2.7

Identifying and mapping very small mountain glaciers on coarse to high-resolution imagery

Joshua Leigh, Chris Stokes, Rachel Carr, Ian Evans, Liss Andreassen, and David Evans

Small mountain glaciers are an important part of the cryosphere and tend to respond rapidly to climate warming. Historically, mapping very small glaciers (generally considered to be <0.5 km2) using satellite imagery has often been subjective due to the difficulty in differentiating them from perennial snowpatches. For this reason, most scientists implement minimum size-thresholds (typically 0.01–0.05 km2). However, when mapping on high-resolution imagery (<1 m) with minimal seasonal snow cover, glaciers <0.05 km2 and even <0.01 km2 are readily identifiable and using a minimum threshold may be inappropriate. For these cases, we have developed a set of criteria to enable the identification of very small glaciers and classify them as certain, probable, or possible. Our identification criteria are based on detailed ice surface structures (e.g. evidence of flow banding and crevasses) and diagnostic glacial landforms (e.g. moraines). Implementation of this scoring system should facilitate a more consistent and objective approach to identifying and mapping very small glaciers on high-resolution imagery, helping to produce more comprehensive and accurate glacier inventories.

How to cite: Leigh, J., Stokes, C., Carr, R., Evans, I., Andreassen, L., and Evans, D.: Identifying and mapping very small mountain glaciers on coarse to high-resolution imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3901, https://doi.org/10.5194/egusphere-egu2020-3901, 2020.

EGU2020-2638 | Displays | CR2.7 | Highlight

Ad hoc estimation of glacier contributions to sea-level rise from latest glaciological observations

Michael Zemp, Matthias Huss, Nicolas Eckert, Emmanuel Thibert, Frank Paul, Samuel U. Nussbaumer, and Isabelle Gärtner-Roer

Comprehensive assessments of global glacier mass changes based on a variety of observations and prevailing methodologies have been published at multi-annual intervals, typically towards IPCC reports. For the years in between, the glaciological method provides annual observations of specific mass changes but is suspected to not be representative at the regional to global scales due to uneven glacier distribution with respect to the full sample. Here, we present a framework to infer ad hoc (i.e., timely but preliminary) estimates of global-scale glacier contributions to sea-level rise from annual updates of glaciological observations. For this purpose, we combine the annual anomaly provided by the glaciological sample (relative to a decadal mean) with the (mean) absolute mass-change rate of a global reference dataset over a common calibration period (from 2006/07 to 2015/16). As a result, we provide preliminary estimates of regional and global glacier mass changes and related uncertainties for the latest hydrological years; i.e. about –300 ± 250 Gt per year in 2016/17 and –500 ± 200 Gt per year in 2017/18. These ad hoc estimates indicate that glacier contributions to sea-level rise exceeded 1 mm SLE per year which corresponds to more than a quarter of the currently observed rise. We also discuss the regional biases of the glaciological sample and conclude with a brief outlook on possible applications and remaining limitations of the glaciological observation network of the World Glacier Monitoring Service.

How to cite: Zemp, M., Huss, M., Eckert, N., Thibert, E., Paul, F., Nussbaumer, S. U., and Gärtner-Roer, I.: Ad hoc estimation of glacier contributions to sea-level rise from latest glaciological observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2638, https://doi.org/10.5194/egusphere-egu2020-2638, 2020.

EGU2020-16031 | Displays | CR2.7 | Highlight

Global Glacier Mass Loss estimated from GRACE and GRACE-FO Satellite Observations (2002-2019)

Bert Wouters, Alex Gardner, Geir Moholdt, and Ingo Sasgen

Glaciers outside of the ice sheets are important contributors to sea level rise. Although their overall mass balances can be estimated by upscaling local field measurement, direct observations with global coverage are only feasible with satellite remote sensing.  Satellite gravimetry of the Gravity Recovery and Climate Experiment (GRACE) showed that between 2002 and 2016, glaciers lost mass at a rate of 199 ± 32 Gt yr−1, equivalent to a cumulative sea level contribution of 8 mm. After about one year of interruption following the end of the GRACE science operations in June 2017, GRACE Follow-On (GRACE-FO) now allows us to extend the time series of its predecessor starting June 2018.

In this work, we provide updated estimates of the global glacier annual mass balance for 2002 and 2019 based on GRACE/GRACE-FO, and present regional changes with a focus on recent years. Furthermore, we discuss the different uncertainties entering our mass balances and compare our estimates to those based on upscaling in-situ measurements.

How to cite: Wouters, B., Gardner, A., Moholdt, G., and Sasgen, I.: Global Glacier Mass Loss estimated from GRACE and GRACE-FO Satellite Observations (2002-2019), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16031, https://doi.org/10.5194/egusphere-egu2020-16031, 2020.

EGU2020-11020 | Displays | CR2.7

Local climate of Zachary glacier, North East Greenland

Carleen Reijmer, Abas Khan, Eric Rignot, Michiel van de Broeke, and Brice Noël

In August 2016, two automatic weather stations (AWS) were placed on Zachary glacier, North East Greenland. They were installed in support of a project investigating the surface mass balance, ice velocity and calving conditions of Zachary glacier. The stations are full energy balance stations, i.e. they measure all parameters (air temperature, wind speed, relative humidity, air pressure, and short and long wave incoming and outgoing radiation) necessary to derive the full surface energy balance. In addition, the stations are equipped with a sonic height ranger in combination with a draw wire to measure snow accumulation and ice melt, respectively, and a GPS to monitor glacier velocity. These stations provide insight in the local climate of north east Greenland, a region for which only limited in situ data is available.

The AWS were located initially at ~145 m a.s.l., about 13 km from the glacier front (AWS23), and at  ~535 m a.s.l., about 35 km from the glacier front (AWS22). Both are moving reasonably fast (0.7 – 1.7 km/yr) towards the front, which has an impact on observed variables mainly since station elevation decreases, although changing (surrounding) topography impacts wind and radiation observations as well. Results show that both sites exhibit a strong katabatic signature, with directional constancies around 0.9, and wind speeds in winter being twice as strong as in summer. Temperature difference between the sites reflect the height difference, and is smaller in summer due to the melting surface impacting the near surface temperature. The lapse rate increases from ~0.5 °C/100 m in summer to ~0.7°C/100 m in the other seasons. The lower station, AWS23, is located in the ablation zone and has experienced on average 2.1 m ice melt over the past 3 years. At the higher station the mass budget appears to be in balance over this period.

The 3.5 years of available station data is compared with regional climate model RACMO2.3p2 output (5.5 km resolution), where monthly averaged data from the grid point nearest to the average station location is used. Initial differences in surface pressure reflect a difference in model grid height and station elevation (stations being located at lower elevation), while an increase in the absolute difference reflects the fast movement of the glacier transporting the AWS to lower elevations (30 and 70 m lowering for AWS22 and 23 respectively). The model overestimates temperature at AWS22 (1.3 °C), and wind speeds are too high at both sites.

How to cite: Reijmer, C., Khan, A., Rignot, E., van de Broeke, M., and Noël, B.: Local climate of Zachary glacier, North East Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11020, https://doi.org/10.5194/egusphere-egu2020-11020, 2020.

EGU2020-18096 | Displays | CR2.7

Garabashi glacier (Caucasus) mass changes estimated from glaciological and geodetic mass balance measurements

Stanislav Kutuzov, Andrey Smirnov, Gennady Nosenko, Ivan Lavrentiev, Aleksei Poliukhov, Nelly Elagina, and Stanislav Nikitin

The ice-covered Europe's largest volcanic massif Elbrus (5,642 m) is a unique object for studying the reaction of mountain glaciers to climate changes. Elbrus glacial system contains more than 10% of the total ice volume in the Greater Caucasus. Elbrus glaciers influence on the recreation development. The rivers runoff from the Elbrus glaciers irrigates agricultural lands on steppe plains of the North Caucasus.

The rate of glacier reduction in the late XX - early XXI centuries has increased significantly and in 1997-2017 Elbrus have lost 23% of its volume. Despite a number of glacier studies the mechanisms and quantitative characteristics surface mass exchange on Elbrus are still uncertain. Mass balance calculations were based on limited data. In particular, amount and distribution of snow accumulation, mass balance sensitivity to meteorological parameters under dramatic climate changes and other parameters remained unknown.

Here we present the results of the detailed analysis of Garabashi glacier mass changes in 1982-2019 using glaciological and geodetic methods. Based on the new data of snow and ablation distribution the mass balance measurement system of Garabashi glacier was improved in 2018-2019. The mass balance over the studied period was also modelled using both temperature-index and distributed energy mass balance models calibrated by in situ measurements and albedo estimates from the remote sensing.

The mass balance of the Garabashi glacier was close to zero or slightly positive in 1982-1997 and the cumulative mass balance was 1 m w.e. in this period. In 1997-2017 Garabashi glacier lost 12.58 m w.e. and 12.92 ± 0.95 m w.e. (−0.63 and −0.65 ± 0.05 m w.e. a−1) estimated by glaciological and geodetic method, respectively. Additional -1.7 m w.e. were lost in 2018-2019. This resulted in an area reduction by 14% and a loss of 27% of glacier volume. The observed glacier recession is driven by the pronounced increase in summer temperatures, especially since 1995, which is accompanied by nearly consistent precipitation rates The increase in incoming shortwave radiation, also played a significant role in the accelerated mass loss of glaciers in Caucasus. This study was supported by the RFBR grant 18-05-00838 a

How to cite: Kutuzov, S., Smirnov, A., Nosenko, G., Lavrentiev, I., Poliukhov, A., Elagina, N., and Nikitin, S.: Garabashi glacier (Caucasus) mass changes estimated from glaciological and geodetic mass balance measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18096, https://doi.org/10.5194/egusphere-egu2020-18096, 2020.

EGU2020-9125 | Displays | CR2.7

Glacier surface elevation changes in Rongbuk Catchment of the Central Himalayas in the last four decades

Qinghua Ye, Wei Nie, Yimin Chen, Gang Li, lide Tian, Liping Zhu, and Jeff S Kargal

Glaciers in the central Himalayas are important water resources for the downstream habitants, and accelerating melting of the high mountain glaciers speed up with continuous warming. We summerized the geodetic glacier surface elevation changes (Dh) by 6 data sets at different time periods during 1974-2016 in RongbukCatchment(RC) on the northern slope of Mt. Qomolangma (Mt. Everest) in the Central Himalayas. The result showed that glacier Dh varied with altitude and time, from -0.29 ± 0.03m a-1 in 1974-2000, to -0.47 ±0.24 m a-1 in 1974-2006,and -0.48 ±0.16 m a-1 in 1974-2012. Dh increased to -0.60 ± 0.20 m a-1 in 2000-2012, then decreased to-0.46 ± 0.24 m a-1 in 2000-2014, and by -0.49 ± 0.08 m a-1 in 2000-2016, showing a diverse rate being up - down- a little up. However, it generally presented a similar glacier thinning rate by -0.46~-0.49 m a-1 in the last four decades since 1970s in RC according to Dh1974-2006, Dh1974-2012, Dh2000-2014, and Dh2000-2016. Local meteorological observations revealed that, to a first order, the glacier thinning rate was kept the same pace with the number of annual melting days (MD). In spite of the obviously arising summer air temperature (TS) in 2000-2014, a slowdown glacier melting rate by -391 mm w.e.a-1 occurred in 2000-2014 because of less melting days with more precipitation and less annual mean temperature(Tm). It shows that MD is another important indicator and controlling factor to evaluate or to estimate glacier melting trend, especially in hydrological or climate modeling.

How to cite: Ye, Q., Nie, W., Chen, Y., Li, G., Tian, L., Zhu, L., and Kargal, J. S.: Glacier surface elevation changes in Rongbuk Catchment of the Central Himalayas in the last four decades, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9125, https://doi.org/10.5194/egusphere-egu2020-9125, 2020.

EGU2020-951 | Displays | CR2.7

Long-term mass balance, runoff and area change in Stok group of glaciers, Ladakh, India, between 1969 to 2019.

Mohd Soheb, Alagappan Ramanathan, and Sonam Lotus

An analysis of mass balance (MB), runoff and area of a group of small glaciers (< 1 km2) in Stok region, Ladakh, India, was conducted to investigate their behaviour in past few decades. These glaciers are essential to the downstream village of ~300 households as they are entirely dependent on the ice and snow meltwater for domestic and agricultural use. The study presents an in-situ (2014-2019) and historical modelled MB (1978-2019) of Stok glacier, which is first of its kind in Ladakh region. The observed MB was found to be negative since 2014 with an average MB of -0.4 m w. e. a-1. However, modelled MB showed a balanced condition during 1980s, followed by a severe retreat in the first decade of 21st century. MB sensitivity analysis suggests that the winter precipitation and summer temperature are almost equally significant in driving mass balance of the glacier and water resources. Around 27% increase in precipitation is required to compensate the melt due to 1°C rise in temperature. Net changes of glacier extent were determined from a detailed manual comparison of remotely sensed imagery acquired between 1969 to 2019 by the high-resolution declassified Corona mission, Landsat ETM+/OLI and PlanetScope satellites. All the glaciers in this region retreated with different rates during different periods. Overall, the reduction in glacier extent was found to be around -0.73 km2 (-0.016 km2 a-1) equivalent to ~15% of the total glacier extent, in the past five decades. Runoff from the catchment was also modelled with the help of available temperature, precipitation and remote sensing data. The runoff model was calibrated and validated using daily in-situ discharge data of two summers (2018 and 2019). It was found that the runoff was highest during July and August months due to both increased snow and ice melt. Winter precipitation in this region is essential not only for glacier health but for early spring sowing season when the demand for the water is highest, and snowmelt water is the only source of early streamflow. Thus, this study assumes greater significance in light of an perceptible shift in precipitation from winter to summer in past two decades, which needs further investigation.

How to cite: Soheb, M., Ramanathan, A., and Lotus, S.: Long-term mass balance, runoff and area change in Stok group of glaciers, Ladakh, India, between 1969 to 2019., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-951, https://doi.org/10.5194/egusphere-egu2020-951, 2020.

EGU2020-3466 | Displays | CR2.7

National glacier monitoring – strengths and weaknesses, responsibilities and priorities

Isabelle Gärtner-Roer, Samuel U. Nussbaumer, Fabia Hüsler, and Michael Zemp

Glaciers impact the lives of millions of people whose drinking water supply, energy production, and irrigation-dependent agriculture is disrupted as the glaciers melt. Knowledge on glacier distribution and quantification of glacier changes is crucial to assessing the impact of glacier shrinkage on the society. Therefore, glacier monitoring is vital to the development of sustainable adaptation strategies in regions with glaciated mountains.

Detailed information on national glacier monitoring, including data on glacier distribution as well on as glacier changes, is compiled in a standardized procedure to summarize and also compare the situation in each of the glacierized countries. The resulting country profiles are assessed in relation to the existing monitoring strategy of the Global Terrestrial Network for Glaciers (GTN-G). Gaps between the current implementation of glacier monitoring and implementation targets are analyzed in a solid gap analysis, which allows countries to be categorized as having poorly developed monitoring, needing improvement, or having well-developed monitoring. By this, it is intended to raise awareness of the challenges for the individual national monitoring systems and to illuminate what future needs might be to improve the situation.

The study is meant to provide a baseline for scientists and decision-makers in international organizations, national governments, and local communities, as they take responsibilities to improve glacier monitoring systems and care about their relevance in decision-making processes.

How to cite: Gärtner-Roer, I., Nussbaumer, S. U., Hüsler, F., and Zemp, M.: National glacier monitoring – strengths and weaknesses, responsibilities and priorities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3466, https://doi.org/10.5194/egusphere-egu2020-3466, 2020.

EGU2020-18972 | Displays | CR2.7

Re-establishing mass balance measurements on Aktru glaciers (Altai).

Andrey Smirnov, Stanislav Kutuzov, Aleksandr Erofeev, Sergey Kopysov, Ivan Lavrentiev, Zamir Abbasov, and Kirill Nikitin

The rate of glaciers decline in the late 20th-early 21st centuries increased substantially. These circumstances are of particular relevance in mountainous areas, where glaciers are one of the most important landscape-forming factors, regulate river flow and serve as a potential source of hazardous processes and phenomena that threaten economic and recreational activities. The Aktru Glaciers (Maliy Aktru since 1962, Leviy Aktru and Vodopadniy since 1977) are the ‘reference’ glaciers of the World Glacier Monitoring Service (WGMS).

The Aktru glacier monitoring programs were suspended in 2012. There were only two glaciers with a continuous series of measurements in Russia. Both of these glaciers are located in the Caucasus. The vast area of Northern Eurasia at the current time is not covered with direct measurement data on glaciers, which does not allow to validate the results of global and regional projections of climate and environmental change and causes serious concern to the scientific community.

Here we present the first results of mass balance measurements on Leviy Aktru glacier re-established in 2019. The detailed accumulation measurements supplemented with new ablation stakes network and AWS enabled calculation of the mass balance of -425 mm w.e. in 2018/19. Ice thickness and bedrock topography was estimated using the GPR measurements. Additionally, the glacier volume changes from 2000 to 2019 were assessed for the region using SRTM-X and Pleiades DEM. The data obtained can be used to validate regional hydrological and mass balance models for Altai mountains.

The Pléiades stereo-pair used in this study was provided by the Pléiades Glacier Observatory initiative of the French Space Agency (CNES).

How to cite: Smirnov, A., Kutuzov, S., Erofeev, A., Kopysov, S., Lavrentiev, I., Abbasov, Z., and Nikitin, K.: Re-establishing mass balance measurements on Aktru glaciers (Altai)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18972, https://doi.org/10.5194/egusphere-egu2020-18972, 2020.

EGU2020-9814 | Displays | CR2.7

Glaciers of Grandes Jorasses: an open-air laboratory for glacier monitoring systems development

Niccolò Dematteis, Daniele Giordan, and Fabrizio Troilo

 

Glaciological phenomena can have a strong impact on human activities in terms of hazards and freshwater supply. Therefore, a scientific observation is fundamental to investigate their current state and recent evolution. To this aim, experimenting innovative scientific survey methodologies and equipment is of primary importance. Strong efforts in this field have been spent in the glacial complex of the Grandes Jorasses massif (Mont Blanc area), where several ice break-offs glacial outburst triggered from the Planpincieux Glacier snout and the Whymper Serac and threatened the underling Planpincieux valley in the past. From 2009, the glacial complex has become an open filed laboratory where a wide set of close-range remote sensing survey systems have been developed and applied to investigate the glacial state and dynamics.

Two continuous monoscopic time-lapse cameras observe the Planpincieux Glacier since 2013. Digital image correlation is applied to the photographs to measure the surface kinematics at different level of detail. During the monitoring, image analysis techniques allowed at classifying the instability processes of the terminus and at estimating the volume of the break-off events. Such investigation revealed the presence of possible break-off precursors and a monotonic relationship between glacier velocity and break-off volume, which might help for risk evaluation.

A robotised total station (RTS) is active since 2009 to monitor the Whymper Serac velocity (Grandes Jorasses Glacier). The operative distance between the total station and targets is approximately 5000 m. A network of several prisms is installed onto the serac, but the extreme conditions related to the high-mountain environment force to replace periodically the stakes that are lost. Besides the RTS, a monoscopic camera acquires hourly images of the serac for surface velocity measurements.

In addition to the permanent monitoring systems, surveys with four different terrestrial interferometric radars have been conducted in the Planpincieux Glacier between 2013 and 2019. Helicopter-borne LiDAR and terrestrial laser scanner provided the DEM of the Planpincieux Glacier in 2014 and 2015 respectively. A sequence of six DEMs has been also produced by aerial and UAV structure from motion in the time span 2017-2019. Finally, a helicopter ground penetrating radar campaign was conducted in 2013 to evaluate the thickness of the Planpincieux Glacier and Whymper Serac.

For what concerns the mountain glaciers, the survey activity conducted in the Grandes Jorasses massif since 2009 is probably one the most intensive and variegated in European Alps. This makes such an environment an open-air laboratory for experimenting close-range remote sensing monitoring systems that it is ready for new research activities and monitoring solutions development.

 

 

How to cite: Dematteis, N., Giordan, D., and Troilo, F.: Glaciers of Grandes Jorasses: an open-air laboratory for glacier monitoring systems development, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9814, https://doi.org/10.5194/egusphere-egu2020-9814, 2020.

EGU2020-18934 | Displays | CR2.7

The new Swiss Glacier Inventory SGI2020: From a topographic to a glaciological dataset

Andreas Linsbauer, Elias Hodel, Matthias Huss, Andreas Bauder, Mauro Fischer, Yvo Weidmann, and Hans Bärtschi

A glacier inventory describes the extent of all glaciers at a given point in time and in periods of rapid glacier change a frequent update is needed. The Swiss Glacier Inventory 2010 (SGI2010) is the last official inventory for Switzerland and was derived by manual digitization from high-resolution (25 cm) aerial orthophotographs from swisstopo (Federal Office of Topography). To regularly produce a revised inventory, based on the high-quality aerial images from swisstopo acquired at a three-year interval, the workload cannot be covered by GLAMOS (Glacier Monitoring Switzerland, www.glamos.ch) on its own. As part of the development of the new topographic landscape model of Switzerland (swissTLM3D), swisstopo introduced – based on requirements defined by GLAMOS – the object class “glaciers”. This secures that Swiss glaciers are recurrently mapped based on high-resolution data on a long term. Swiss Glacier Inventories can therefore be derived by GLAMOS from the TLM object class “glaciers”.

The SGI2020 is the first glacier inventory produced by GLAMOS based on the new workflow and stands out with an unprecedented level of detail regarding glacier mapping. As the glacier-excerpt from the swisstopo TLM is a landcover dataset, produced according to guidelines for topographical purpose, it does not fit all glaciological requirements. Here, we present the necessary steps and adjustments to derive a new glacier inventory for the period 2013-2018 that fits all glaciological criteria. Furthermore, we compare the resulting dataset with former SGI’s and pin down the major changes and differences emerging from different methodologies used. We particularly emphasize on problematic definitions of glacier boundaries related to snow coverage and/or supraglacial debris and provide updated results for glacier area changes in the Swiss Alps over the last decades.

How to cite: Linsbauer, A., Hodel, E., Huss, M., Bauder, A., Fischer, M., Weidmann, Y., and Bärtschi, H.: The new Swiss Glacier Inventory SGI2020: From a topographic to a glaciological dataset, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18934, https://doi.org/10.5194/egusphere-egu2020-18934, 2020.

EGU2020-9888 | Displays | CR2.7

A new working group on the Randolph Glacier Inventory (RGI) and its role in future glacier monitoring

Fabien Maussion, Regine Hock, Frank Paul, Philipp Rastner, Bruce Raup, and Michael Zemp

The Randolph Glacier Inventory (RGI) is a globally complete collection of digital glacier outlines, excluding the two polar ice sheets. It has become a pillar of glaciological research at global and regional scales, among others for estimates of recent and future glacier changes, glacier mass balance, and glacier contribution to sea-level rise. After its creation in 2012, the dataset’s further development has been coordinated by an IACS Working Group (WG) until 2019. This new WG (2020 - 2023) expands the scope of the previous one with new and updated objectives.

The latest RGI version (V6) was released in July 2017, and several new glacier outline datasets have been generated by the community since then. In the past, the RGI was updated by an ad-hoc manual process, which was effective but labor-intensive. One of the main objectives of the WG is to automate this process as much as possible by incorporating RGI generation tools into the Global Land Ice Measurements from Space (GLIMS) glacier database. Furthermore, the RGI (as of version 6) needs further improvements  to remain useful to the wider scientific community. Examples include data quality (wrong/outdated outlines, ice divides) but also the quality and availability of glacier attributes (hypsometry, glacier type, ...). Additionally, there is a demand for consistent historic glacier outlines (e.g. from the mid-1980s or earlier) to facilitate validation of glacier evolution models or transient mass balance calculations. With this WG, we strive to continuously improve and update the RGI, as well as to lay out a long-term plan for sustainable continuation of the RGI beyond the end of this WG.

In this presentation, we will discuss the current status and future of the RGI, and will engage with the community to encourage participation and feedback.

How to cite: Maussion, F., Hock, R., Paul, F., Rastner, P., Raup, B., and Zemp, M.: A new working group on the Randolph Glacier Inventory (RGI) and its role in future glacier monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9888, https://doi.org/10.5194/egusphere-egu2020-9888, 2020.

EGU2020-12515 | Displays | CR2.7

The need for global glacier speed to combine measured velocity with balance velocity

Hester Jiskoot, Easton DeJong, Wesley Van Wychen, and Jade Cooley

One of the outstanding glaciological research questions is how glaciers respond dynamically to climate change and how this varies regionally. Ice-velocity changes occur on an interannual scale in response to mass-balance forcing changing the glacier geometry and therefore the driving stress. For a glacier tending towards steady-state the mass flux through a cross-section equals the mass balance upstream of the cross-section. Mass loss will, therefore, usually lead to a slowdown of glaciers. However, a changing climate can also affect the occurrence of sliding and change a glacier’s thermal regime and its marginal processes (ice-ocean, ice-lake and ice-bed interactions). The response of glacier flow to climate change is, therefore, not straightforward, and mass loss combined with increased meltwater production or a transition to a temperate regime may lead to an increase in flow speed. Ultimately, depending on their individual response time, glaciers respond in a delayed dynamical way to changes in mass balance.

Various recent publications have addressed the above research question at regional scales by analysing decadal changes in flow speed in relation to glacier mass loss. Only few local works, however, have addressed the question in the context of measured differences between actual and balance velocities. The recent generation of diverse global glacier datasets, such as the Randolph Glacier Inventory (RGI), GoLIVE and ITS_LIVE ice speed, ice thickness, and globally-distributed datasets such as WGMS mass balance data and companion ground measurements, offer opportunities to address outstanding research questions in interregional to global perspectives. We will compare, for the first time, for glaciers in various RGI subregions the difference between the measured glacier velocity, derived from available GoLIVE and ITS-LIVE datasets and additional speckle tracking from SAR scenes, and the balance velocity, derived using mass balance profiles, hypsometry, and ice thickness datasets. We use the standard approach of deriving balance flux along a flowline, and use a scenario-based approach to deal with measurement and model uncertainties. In this poster we present the results for approximately 20 glaciers in Canada and Iceland in detail. Ultimately, we aim to use more than 200 glaciers with WGMS and independent long-term mass balance records, distributed over the 19 RGI first-order regions and as many as the 89 second-order regions as possible.

How to cite: Jiskoot, H., DeJong, E., Van Wychen, W., and Cooley, J.: The need for global glacier speed to combine measured velocity with balance velocity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12515, https://doi.org/10.5194/egusphere-egu2020-12515, 2020.

EGU2020-10734 | Displays | CR2.7

Glacial reduction in the Gran Paradiso Massif (Western Italian Alps): multitemporal dynamic inventory since the Little Ice Age

Simona Gennaro, Maria Cristina Salvatore, Linda Alderighi, Riccardo Cerrato, and Carlo Baroni

Alpine glaciers are sensitive key markers of climate variations, as their geometry and shape are the results of adjustments in response to changes of their mass balance. Since the Little Ice Age the European Alps, as well as other mountain ranges, experienced a phase of generalized retreat, accentuated during the last decades. The availability of quantitative data on glaciers variations from major mountain regions represent relevant tools for better understanding the glacier behaviour in response to ongoing climatic changes. Here we present new data on Holocenic variations of glaciers hosted in the Gran Paradiso Massif, the first Italian National Park (Western Italian Alps).

We built the multi-temporal digital inventory of the Gran Paradiso Massif glaciers covering a time period of over 150 years, considering distinct time steps spanning from the Little Ice Age (LIA) to 2015. The multi-temporal dataset was built including glaciers outlines (derived from high resolution orthophotos and historical maps) and the data related to frontal variations (coming from annual glaciological surveys conducted by the Italian Glaciological Committee). Database was managed in GIS environment and populated following the guidelines suggested by the WGMS. Multi-temporal analysis supplied new quantitative data on the strong glacial decline occurred since the LIA and dramatically accelerated since the 90s.

During the LIA the Gran Paradiso Massif hosted more than 120 glaciers extended for about 112 km2 reduced to 73 units in 2015 covering only about 32 km2.

Our data underline a loss of about 50 ± 4 m w.e. and ELA variations of about 166/130 ± 5/4 m (considering AAR/AABR methods, respectively) from the maximum LIA position and 2006. The strong contraction and fragmentation of the studied glaciers is underlined by area loss of over 71% (with a reduction rate of -0.36% y-1) from the LIA to 2015, as well as by the increase in the number of glacial bodies smaller than 0.1 km2, and by the increase in the number of extinct glaciers (33 in 2015 respect to 1957). Furthermore, during the last decades, new data obtained show a dramatic acceleration in the contraction rates of the glacial bodies, which can lead to impressive landscape changes and to a relevant increase of geomorphological hazard.

The multitemporal data show a very detailed evolution of Gran Paradiso glaciers also considering ice- mass loss and can contribute to modelling glaciers response to climate changes in a sensitive area of the Italian Alps, considering its location at the border of a “dry zone”. Improving the knowledge on the glacial resource could contribute in better understanding the impact of warming climate on mountain hydrology, as well as to increase the awareness of the population and authorities to be resilient in a near future with strong reduction of meltwater runoff.

How to cite: Gennaro, S., Salvatore, M. C., Alderighi, L., Cerrato, R., and Baroni, C.: Glacial reduction in the Gran Paradiso Massif (Western Italian Alps): multitemporal dynamic inventory since the Little Ice Age , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10734, https://doi.org/10.5194/egusphere-egu2020-10734, 2020.

EGU2020-18666 | Displays | CR2.7

Change in Mt. Elbrus nival-glacial system in the last century

Sergey Sokratov, Yuri Seliverstov, Alla Turchaniniva, Evgenii Kharkovets, and Heitor Evangelista da Silva

We investigated the long-term dynamics of four glaciers that are part of the nival-glacial system of Mount Elbrus and located on its southern slope: Terskol, Garabashi, Malyi Azau, Bol’shoi Azau. The time period of the study covers 1887–2017. Glaciological measurements were carried out using DEM, compiled from early-year maps and from the results of stereo surveys in 2017, made by UAVs and high-resolution digital camera. New results present the change in the area of these glaciers, the elevation of their lowest points and the height of the surface. All these characteristicsindicate decrease of glaciation at the southern slope of Elbrus and intensification of this process in the last decade. Some differences in dynamics of changes of different glaciers can be explained by differences in their morphological types, morphometric indicators, the state of the beds, which we do not have much information about. Additionally, cores of two near glaciers lakes sediments were extracted and analyzed, offering high resolution record of sedimentation. The age of the bottom lake sediments near Malyi Azau glacier corresponds to documented beginning of the lake formation due to glacier ice retreat in 1950th. The other lake to the side of the Garabashi glacier was formed much earlier and the upper 15 cm of the lake sediments core is formed between 1893 and 2016.

The obtained results are compared with the results of other investigations. We believe that the new data of glaciers dynamics is more accurate and more promising in understanding the specific of accumulation and melt in dependence on elevation, slopes aspect s and angle.

How to cite: Sokratov, S., Seliverstov, Y., Turchaniniva, A., Kharkovets, E., and Evangelista da Silva, H.: Change in Mt. Elbrus nival-glacial system in the last century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18666, https://doi.org/10.5194/egusphere-egu2020-18666, 2020.

EGU2020-9339 | Displays | CR2.7

The state of Kersten Glacier and the Northern Icefield on Mt. Kilimanjaro

Catrin Stadelmann, Johannes Fürst, Thorsten Seehaus, Thomas Mölg, and Matthias Braun

The glaciers on Kilimanjaro are unique indicators for climatic changes in the tropical mid-troposphere of Africa. Glaciers in the tropics have shown a severe retreat since the Last Glacial Maximum and the glaciers on Mt. Kilimanjaro are no exception, with an 85% reduction in glacier area from 1912 to 2013. This history of severe glacier area loss raises concerns about an imminent future disappearance. Yet, the remaining ice volume is not well known.

By combining state-of-the-art techniques from satellite remote sensing and glacier mass balance modelling with data assimilation, we inferred the  glacier ice thickness of two selected glaciers on Mt. Kilimanjaro. We reconstruct thickness maps for 2000 and 2011 for the Northern Icefield and Kersten Glacier and find mean thickness values of 26.6 and 9.3 m for 2011, respectively. Model validation was difficult for Kersten Glacier, as no ice thickness  measurements were available. Thus, the first attempt to use decadal retreat information, to infer past glacier ice thickness, which are used to do a glacier-specific calibration of the ice thickness reconstruction, was conducted by creating a generic margin thickness from glacier outlines and DEM differencing. This approach proved to be reasonable for Kersten Glacier, where a more common glacier type was assumed, but seemed to underestimate ice thickness at the Northern Icefield, because of the complex topography.

The poster summarizes the results obtained from the thickness reconstructions and compares them to thickness maps from an existing global consensus estimate. In comparison to our results the consensus estimate shows unrealistically thick values for KG in areas that are meanwhile ice-free. A rough projection on glacier recession based on the generated thickness data agrees with other estimates pointing towards the disappearance of the glaciers between 2040 and 2060.

How to cite: Stadelmann, C., Fürst, J., Seehaus, T., Mölg, T., and Braun, M.: The state of Kersten Glacier and the Northern Icefield on Mt. Kilimanjaro , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9339, https://doi.org/10.5194/egusphere-egu2020-9339, 2020.

Svalbard is dominated by large (often calving) glaciers and ice caps with a strong contribution to global sea-level rise. Due to many surge-type glaciers, large changes of glacier extents are common and determination of their mass balance requires a regular update of their outlines. However, frequent cloud cover prevents accurate repeat mapping. In consequence, the last glacier inventory for Svalbard was compiled from satellite scenes acquired over a period of 11 years, making change assessment and other applications difficult. Due to long-lasting seasonal snow and confusion with large perennial snow patches, the minimum size of this inventory has been set to 1 km2.

Here we present a new glacier inventory for Svalbard that has been compiled at 10 m resolution from two Sentinel-2 scenes that were acquired only two days apart. Sea ice, ice-bergs, lakes and turbid water were wrongly classified as glaciers by the applied band ratio method and manually removed. Debris cover, snow and ice under some clouds but also polluted (very dark) clean ice was not mapped as thresholds were optimized to get snow and ice in shadow properly mapped. These missing regions were manually added. Snow patches were removed with a 5 by 5 majority filter applied to the binary glacier map and a minimum size of 0.05 km2. Outlines from the previous inventory as available in the RGI were used to guide the corrections. After careful comparison, we used the Arctic DEM to derive surface drainage divides and topographic attributes for all glaciers.

The largest challenges for accurate glacier delineation are discrimination of debris-covered glaciers from peri-glacial debris and rock glaciers, handling of attached seasonal or perennial snowfields, and identifying disintegrating tongues of down-wasting and often debris-covered ice masses remaining after a surge. Compared to the previous inventory, the large area gains and losses of surge-type glaciers are remarkable, but area differences result also from a different interpretation of debris-covered glaciers, inclusion of snow-filled couloirs and several new glaciers that were excluded in the previous inventory.

How to cite: Paul, F. and Rastner, P.: Glacier mapping with Sentinel-2 in Svalbard: Challenges when creating a new glacier inventory in the Artic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11403, https://doi.org/10.5194/egusphere-egu2020-11403, 2020.

EGU2020-11059 | Displays | CR2.7

Which DEM to use for glacier inventory applications? The example of Svalbard

Philipp Rastner and Frank Paul

Creating glacier inventories from satellite images and a digital elevation model (DEM) has become quasi standard. Besides the specific challenges for glacier mapping, also the selection of the ‘best’ DEM can be difficult. When using it to derive surface drainage divides and topographic information for each glacier, one has to consider the date of acquisition, artefacts, spatial completeness (data voids) and resolution. In general, using different DEMs gives different drainage divides and thus other glacier sizes. Moreover, due to widespread glacier retreat and rapid surface lowering, topographic information from older DEMs is increasingly biased towards too high values.

In this study we analyse seven freely available DEMs for the Arctic region of Svalbard: ALOS AW3D30, two National Elevation Datasets (NEDs), Arctic DEM, TanDEM-X (90 and 30 m products) and the ASTER GDEM2. All individual DEM tiles were mosaicked and re-projected bilinearly to UTM 33 N. Comparisons of topographic data are performed for three test regions: a) stable terrain (off glaciers), b) glaciers in rough topography, and c) flat glaciers and ice caps.

Overlay of drainage divides indicate large area differences on flat ice caps and small ones in rough topography, where mountain ridges are distinct. On the other hand, different spatial resolution results in large differences in rough topography but plays only a minor role for flat topography. Only 2 m elevation differences on stable terrain in flat valley bottoms were detected between the ALOS DEM (79.9m) and the two NEDs (77.9 m). No differences were found between the TanDEM-X 90 / 30 m and the Arctic DEM (all 109. 9 m). The ellipsoid-geoid difference is thus ~30 m in this region.

Mean elevations of glaciers with flat topography or ice caps differ only slightly, but in steeper topography they reach 6 to 8 m. These differences are also due to the different resolution of the DEMs. In all test regions, only small gaps are detected in the Arctic DEM and artefacts are especially present in the ALOS DEM. For this region the ‘best’ DEM is the TanDEM-X DEM.

How to cite: Rastner, P. and Paul, F.: Which DEM to use for glacier inventory applications? The example of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11059, https://doi.org/10.5194/egusphere-egu2020-11059, 2020.

EGU2020-15184 | Displays | CR2.7

Low-elevation of Svalbard glaciers drives high mass loss variability

Brice Noël, Constantijn Jakobs, Ward Van Pelt, Stef Lhermitte, Bert Wouters, Carleen Reijmer, Willem Jan Van de Berg, and Michiel Van den Broeke

With a maximum in glaciated area below 450 m elevation (peak in the hypsometry), most Svalbard glaciers currently experience summer melt that consistently exceeds winter snowfall. Consequently, these glaciers can only exist through efficient meltwater refreezing in their porous firn layers. Before the mid-1980s, refreezing retained 54% of the meltwater in firn above 350 m. In 1985-2018, atmospheric warming migrated the firn line upward by 100 m, close to the hypsometry peak, which triggered a rapid ablation zone expansion (+62%). The resulting melt increase in the accumulation zones reduced the firn refreezing capacity by 25%, enhancing runoff at all elevations. In this dry climate, the loss of refreezing capacity is quasipermanent: a temporary return to pre-1985 climate conditions between 2005 and 2012 could not recover the meltwater buffer mechanism, causing strongly amplified mass loss in subsequent warm years (e.g. 2013), when ablation zones extend beyond the hypsometry peak.

How to cite: Noël, B., Jakobs, C., Van Pelt, W., Lhermitte, S., Wouters, B., Reijmer, C., Van de Berg, W. J., and Van den Broeke, M.: Low-elevation of Svalbard glaciers drives high mass loss variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15184, https://doi.org/10.5194/egusphere-egu2020-15184, 2020.

EGU2020-4927 | Displays | CR2.7

Alpine glaciers disappearance tipping point: results from EURO-CORDEX models

Enrico Scoccimarro and Danile Peano

The front variations of Alpine glaciers show a general retreat over the past 150 years. This glacier retreat, then, has a large impact on many regional sectors, such as hydroelectricity production, river runoff, and touristic sector. In the last decades, glacier retreat in the Alps has been extremely evident due to the pronounced temperature increase affecting these mountains.

Moreover, numerous model studies exhibit a high probability of occurrence of Alpine glacier disappearance by the end of the current century, especially under extreme future climate change conditions.

The Alpine glaciers disappearance is expected to largely influence the Alpine glaciers regions climate, especially in terms of water availability. For this reason, the occurrence of the Alpine glaciers disappearance is enumerated among the climate tipping point.

Given the reduced average glaciers dimension, high-resolution data are needed to investigate the occurrence and the potential impacts of this tipping point. Thus, the EURO-CORDEX dataset over the EUR-11 domain are analyzed in this study.

Alpine glaciers differ under many characteristics, such as elevation, mean aspect, length, and shape. Consequently, a minimal glacier model, which takes into account few glacier features, is used in detecting the occurrence of the Alpine glaciers disappearance. Besides, a simplified surface mass balance model contributes to generalize the tipping point detection and assess the expected water budget changes.

This effort is part of the EU-funded COACCH project.   

 

Keywords

 

Alpine Glaciers, tipping point, water cycle, EURO-CORDEX

How to cite: Scoccimarro, E. and Peano, D.: Alpine glaciers disappearance tipping point: results from EURO-CORDEX models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4927, https://doi.org/10.5194/egusphere-egu2020-4927, 2020.

EGU2020-13068 | Displays | CR2.7

Modelling future glacier evolution: Which feedbacks are relevant?

Matthias Huss, Enrico Mattea, Andreas Linsbauer, and Martin Hoelzle
Numerous models to project the future evolution of mountain glaciers in response to ongoing climate change are available, both at the local and the global scale. However, a suite of partly major simplifications is necessary in these models given the restrictions in data availability. Whereas most models account for the primary feedbacks, such as the snow-ice albedo feedback and the dynamic glacier response in some way, a considerable number of yet poorly understood or less investigated feedbacks is present that might significantly hamper the reliability of current glaciological projections.
 
Here, we present results of a detailed modelling study for the example of Vadret da Morteratsch, Swiss Alps. A surface mass balance model accounting for ice dynamics is forced with downscaled regional climate model output (68 scenarios, CH2018) for the period 2015 to 2100. Various processes are either parameterized or explicitly accounted for. We focus on the use of a fully distributed surface energy-balance approach in comparison to simplified degree-day methods. The relevance of projected changes in different components of the energy balance is assessed using model experiments. In particular, the importance of feedback effects due to (1) the spatio-temporal evolution of supraglacial debris, (2) the formation of new proglacial lakes, and (3) changes in bare-ice albedo and local direct solar irradiance is investigated.
 
We find that the above feedback effects all have a rather small potential to substantially impact on the rates of expected glacier retreat. In some cases, this is unexpected (e.g. for debris coverage and proglacial lakes) but can be explained by compensating processes. We also discuss and visualize the future wastage of Vadret da Morteratsch under the newest generation of climate scenarios, and put these results into context with previous studies, as well as with plans to artificially reduce the rate of glacier mass loss.

How to cite: Huss, M., Mattea, E., Linsbauer, A., and Hoelzle, M.: Modelling future glacier evolution: Which feedbacks are relevant?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13068, https://doi.org/10.5194/egusphere-egu2020-13068, 2020.

EGU2020-13289 | Displays | CR2.7

Forecasting alpine glacier evolution at the seasonal/multiannual scale

Marta Chiarle, Roberta Paranunzio, Guido Nigrelli, Giovanni Mortara, Silvia Terzago, Jost von Hardenberg, and Chiara Cardinali

For application purposes (in particular water resources management and planning) it is crucial to rely on accurate predictions of the evolution of glaciers on short time scales (from seasonal to multi-annual).

This is one of the aims of the MEDSCOPE project in the framework of the ERA4CS initiative: seasonal-to-decadal climate forecasts, produced and downscaled by the project, are used to estimate the evolution of glaciers in selected areas of the Western Italian Alps.

For this purpose, empirical glacier models have been calibrated with historical observational data of glacier front fluctuation and mass balance for five glaciers, characterized by different morphology and topoclimatic setting, in the Western Italian Alps. The models will be forced with the seasonal, downscaled forecasts, in order to assess the added value provided by MEDSCOPE to climate services for water management.

How to cite: Chiarle, M., Paranunzio, R., Nigrelli, G., Mortara, G., Terzago, S., von Hardenberg, J., and Cardinali, C.: Forecasting alpine glacier evolution at the seasonal/multiannual scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13289, https://doi.org/10.5194/egusphere-egu2020-13289, 2020.

EGU2020-3425 | Displays | CR2.7

Development of basinal scale glacier mass balance model: an approach based on satellite observation and energy balance components

Akansha Patel, Ajanta Goswami, Thamban Meloth, and Parmanand Sharma

The understanding of fresh water storage in the Himalayan region is essential for water resource management of the region. As glacier mass balance is a difference between the input and output water storage in a glacier over a period, glacier mass balance can be used as an indirect method to understand the storage. In the northwestern Himalaya, microscale meteorological stations are needed for mass balance estimation due to rugged terrain and complex topography of this region. However, there are only few meteorological stations available in that region. Therefore, in this study, we have developed a new model for glacier mass balance estimation at basinal scale. This model  includes the parameterization of energy balance components viz. albedo, longwave radiation, shortwave radiation, sensible heat, latent heat and heat flux at spatial and temporal scale using earth observation data. The modeling of air temperature is performed using the multi-regression analysis over the Chenab basin of the Indian Himalayas. Simulation is driven with the 16-days Landsat optical and thermal data from 2015 to 2018 that can be used for parameterization of the variable. This model is calibrated and validated with the field data of period 2015-2016. Further, the impact of climatic change and their influence on mass balance was also assessed to understand the future glacier health and mass changes. In contrast to previous temperature index based basin scale models, this model includes most of the energy balance components for better estimation of glacier mass balance. The model can also be used to estimate possible responses of the world’s glaciers to future climate change.

How to cite: Patel, A., Goswami, A., Meloth, T., and Sharma, P.: Development of basinal scale glacier mass balance model: an approach based on satellite observation and energy balance components, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3425, https://doi.org/10.5194/egusphere-egu2020-3425, 2020.

EGU2020-18265 | Displays | CR2.7

Towards elaboration of a surface mass balance model of a mountain glacier using a stochastic weather generator

Taisiya Dymova, Oleg Rybak, and Viktor Popovnin

Mathematical modeling of surface mass balance (SMB) of mountain glaciers requires appropriate climatic forcing. Normally, meteorological records from the weather stations located as close as possible to the glacier are used for this purpose. In the ideal case, a weather station is located directly on the glacier. Even then, weather records are comparatively short and are hardly applicable for transient simulation of glacier dynamics. Thus, the lack of observations is an obvious obstacle for obtaining reliable simulation results. To overcome it, we suggest to apply a simple stochastic weather generator to emulate synthetic records of surface air temperature, precipitation and other meteorological variables required for calculation SMB by an energy-balance model.

Weather generators have been applied in many geophysical applications for decades, except, paradoxically, for glaciological ones. This is a powerful tool enabling generation of synthetic records which are statistically similar to observations (including probability distribution, standard deviations, autocorrelations etc.).

We report about the work in progress, which aims at elaboration of a reliable methodology for SMB calculation in diverse environmental conditions.

The study was supported by Russian Foundation of Basic Research RFBR (grant Nos. 18-05-00420 and 18-05-60080).

How to cite: Dymova, T., Rybak, O., and Popovnin, V.: Towards elaboration of a surface mass balance model of a mountain glacier using a stochastic weather generator, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18265, https://doi.org/10.5194/egusphere-egu2020-18265, 2020.

EGU2020-18937 | Displays | CR2.7

Non-climatic factors affecting glacier mass balance (on the example of avalanche nourishment)

Alla Turchaninova, Sergey Sokratov, Yury Seliverstov, Dmitry Petrakov, Anton Lazarev, and Ekaterina Bashkova

Glacier mass balance is affected by non-climatic factors such as topography, debris cover and geometric parameters of glaciers themselves, avalanche activity, volcanism, etc. The contribution of snow avalanches to the snow accumulation on a glacier is still among the least studied components of the glacier’s mass balance. We propose a possible approach for the numerical assessment of snow avalanche contribution to accumulation at mountain glaciers. The approach consists on the following steps: terrain analysis; weather data analysis; snow avalanche volume assessment during an analyzed balance year; numerical simulation of snow avalanches using RAMMS; evaluation of snow avalanche contribution to glacier accumulation. The proposed methodology was tested on three glaciers (Batysh Sook, № 354, Karabatkak) with an area up to 6,5 km2 in the Inner Tien Shan and Kolka glacier with an area 1,2 km2 in the Central Caucasus. To evaluate snow avalanche contribution to the winter accumulation, we reconstructed avalanche release zones that were most probably active during the analyzed balance year and corresponding snow fracture height in each zone. The numerical simulations of most probable released snow avalanches during the analyzed year using avalanche dynamics RAMMS software were performed and compared with the field observations and UAV orthophoto images. The outlines of avalanches deposits were realistically reproduced by RAMMS according to the results of field observations. The estimated contribution of snow avalanches to the accumulation on the studied glaciers during the analyzed balance year was as follows: Batysh Sook – 7,4±2,5%; № 354 – 2,2±0,7%; Karabatkak– 10,8±3,6% of the winter mass balance. In strong contradiction to the benchmark glaciers in the Tien Shan, the Kolka glacier demonstrates rapid mass gain in the Caucasus. It might be explained by significant, up to 80% share of avalanche nourishment to glacier mass gain. We note that avalanche-fed glaciers seem to be more stable at current stage of regional warming observed both in the Caucasus and the Tian Shan. The obtained results show the importance of the non-climatic factors for glacier surface mass balance control.

How to cite: Turchaninova, A., Sokratov, S., Seliverstov, Y., Petrakov, D., Lazarev, A., and Bashkova, E.: Non-climatic factors affecting glacier mass balance (on the example of avalanche nourishment), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18937, https://doi.org/10.5194/egusphere-egu2020-18937, 2020.

The worldwide glacier is retreating and is expected to continue shrinking in a warming climate. Understanding the dynamics of glaciers is essential for the knowledge of sea-level rise, water resources in high mountain and arid regions, and the potential glacier hazards. Over the past decades, various 3D higher-order and full-Stokes ice flow models including thermomechanical coupling have been developed, and some have opened their source codes. However, such 3D modeling requires detailed datasets about surface and bedrock topography, variable climatic conditions, and high computational cost. Due to difficulties in measuring glacier thickness, only a small minority of glaciers around the globe have ice thickness observations. It is also a challenge to downscale the climate data (e.g., air temperature, precipitation) to the glacier surface, particularly, in rugged high-mountain terrains. In contrast to 3D models, flowline models only require inputs along the longitudinal profile and are thus computationally efficient. They continue to be useful tools for simulating the evolution of glaciers and studying the particular phenomena related to glacier dynamics. In this study, we present a two-dimensional thermomechanically coupled ice flow model named PoLIM (Polythermal Land Ice Model). The velocity solver of PoLIM is developed based on the higher-order approximation (Blatter-Pattyn type). It includes three critical features for simulating the dynamics of mountain glaciers: 1) an enthalpy-based thermal model to describe the heat transfer, which is particularly convenient to simulate the polythermal structures; 2) a drainage model to simulate the water transport in the temperate ice layer driven by gravity; 3) a subglacial hydrology model to simulate the subglacial water pressure for the coupling with the basal sliding law. We verify PoLIM with several standard benchmark experiments (e.g., ISMIP-HOM, enthalpy, SHMIP) in the glacier modeling community. PoLIM shows a good performance and agrees well with these benchmark results, indicating its reliable and robust capability of simulating the thermomechanical behaviors of glaciers.

How to cite: Wang, Y. and Zhang, T.: PoLIM: an open source 2D higher-order thermomechanically coupled mountain glacier flow model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21050, https://doi.org/10.5194/egusphere-egu2020-21050, 2020.

Alfred Wegener contributed extraordinarily to early days of scientific explorations in Greenland. Involved in three expeditions, we present unique historical data that is stored at Graz University, where Wegener filled his last academic position until his tragic death in Greenland in 1930. In this contribution we reevaluate data from his last expedition 1929-1931 acquired at the Qaamarujuup Glacier in West Greenland (71°09'N; 51°11'W). Sub-weekly ablation measurements along with air temperature, humidity, pressure, wind and short-wave radiation data exist for two full ablation seasons both near sea level and in 950 m a.s.l.. The 20th Century reanalysis product of the nearest grid-point performs well reproducing air temperature variability. Coincidentally, this expedition was carried out during a very warm period that was in fact comparable to recent years. We compare vertical ablation gradients from the years 1929/1930 obtained at Qaamarujuup in West Greenland with recent observations from the closest PROMICE automated weather station and discuss differences in a centennial perspective. Furthermore, we present a time-series of glacier stages from the little ice age (LIA) maximum up to present and quantify area and volume changes since. The glacier margin was in close proximity (<50 m distance) to the ocean during the LIA maximum, 660 m and almost 3 km horizontal distance from the ocean in 1930 and in 2019, respectively. Such a drastic geometrical change manifests in differing drivers of the glacier boundary layer with the impact of the cooling ocean during summer decreasing with time as the glacier margin’s distance to the ocean increases. We discuss the potential in using historical glacio-meteorological measurements along with a detailed glacier history in order to extract geometrical feedbacks from the climate change signal.

How to cite: Abermann, J., Schöner, W., and Fausto, R. S.: Historical ablation rates and their drivers in Greenland – assessing the potential of the Wegener expedition for modern glaciological research, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10032, https://doi.org/10.5194/egusphere-egu2020-10032, 2020.

EGU2020-12902 | Displays | CR2.7

Recent temperature history of the Juneau Icefield

Michaela Mühl, Bradley R. Markle, Andreas Gschwentner, Charlie Daniels, Ona Underwood, Abigail Lambert, Paola Araya, Jacquelyn Bellefontaine, Brendon Owczarek, Stanley Pinchak, Alf Pinchak, Robert Asher, Chris McNeil, Scott McGee, and Shad O’Neel

Recent temperature history of the Juneau Icefield

 

Mass loss from Alaskan glaciers makes a significant contribution to current sea-level rise. The Juneau Icefield (JIF) of southeast Alaska is one of the world largest, and longest-studied, ice fields, and is currently in a documented state of thinning, retreat, and negative mass balance. The climatological context of this glacier change is critical to understanding its causes, the future of the region, and perhaps that of similar mountain glaciers. Do these changes primarily reflect changes in accumulation or ablation? Are mean air temperatures in the region increasing? If so, during which season, ablation or accumulation, are the changes strongest?

Here we investigate the recent temperature history of the Juneau Icefield, using a combination of reanalysis data and in situ temperature observations from the Juneau Icefield Research Program.  On the whole, we find a significant trend in annual average temperature since the 1950’s of 0.19°C per decade. Interestingly, this warming is entirely a winter-season signal. We find no significant trend in summer-season temperatures, but a winter time trend of nearly 0.5°C per decade, over twice that of the annual average. This pattern is consistent between the reanalysis products and the local temperature observations across the icefield. Using the in situ measurements from stations across the icefield, we find that the magnitude of the winter-season warming (and that of the annual mean warming) depends strongly on surface elevation: the higher the surface elevation the larger the trend in warming. These results have implications for the cause of recent glacier changes. While there is little evidence for a change in ablation-season temperatures, these results point toward changes in both the length of the ablation season and perhaps the phase of winter precipitation. The elevation-dependence of these trends may have further implications for the future stability of the JIF.

How to cite: Mühl, M., Markle, B. R., Gschwentner, A., Daniels, C., Underwood, O., Lambert, A., Araya, P., Bellefontaine, J., Owczarek, B., Pinchak, S., Pinchak, A., Asher, R., McNeil, C., McGee, S., and O’Neel, S.: Recent temperature history of the Juneau Icefield, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12902, https://doi.org/10.5194/egusphere-egu2020-12902, 2020.

EGU2020-1844 | Displays | CR2.7

Streaming flow on polythermal mountain glaciers: In-situ observations on Jarvis Glacier, Alaska

Ian Lee, Robert Hawley, and Christopher Gerbi

Accelerated melting of glaciers and ice caps has raised serious concerns about sea level rise. As we work towards a solution to address these concerns, it has become a chief priority to rapidly improve predictions of future changes in global ice mass balance. Numerical simulations projecting ice loss have uncovered a strong sensitivity to mechanical and/or rheological weakening of the shear margins of streaming ice. To accurately project sea level rise, future models will require careful treatment of shear margins. This necessitates a deeper understanding of the flow dynamics at shear margins and how streaming flow relates to the constitutive flow law for ice.

 

We developed an open source inexpensive tilt sensor (∼20% the cost of commercial sensors) for studying ice deformation and installed our tilt sensor systems in two boreholes drilled close to the shear margin of Jarvis Glacier, Alaska to obtain kinematic measurements of streaming ice. We used the collected tilt data to calculate borehole deformation by tracking the orientation of the sensors over time. The sensors' tilts generally trended down-glacier, with an element of cross-glacier flow in the borehole closer to the shear margin. We also evaluated our results against flow dynamic parameters derived from Glen's exponential flow law and explored the parameter space of the stress exponent n and enhancement factor E. Comparison with values from ice deformation experiments shows that the ice on Jarvis is characterized by higher n values than that is expected in regions of low stress, particularly at the shear margin (~3.4). The higher n values could be attributed to the observed high total strains coupled with potential dynamic recrystallization, causing anisotropic development and consequently sped up ice flow. Jarvis' n values place the creep regime of the ice between basal slip and dislocation creep. Tuning E towards a theoretical upper limit of 10 for anisotropic ice with single-maximum fabric reduces the n values by 0.2.

How to cite: Lee, I., Hawley, R., and Gerbi, C.: Streaming flow on polythermal mountain glaciers: In-situ observations on Jarvis Glacier, Alaska, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1844, https://doi.org/10.5194/egusphere-egu2020-1844, 2020.

EGU2020-5581 | Displays | CR2.7

A multi-scale investigation of geometrically derived z0 from Hintereisferner, Austrian Alps

Joshua Chambers, Mark Smith, Thomas Smith, Duncan Quincey, Jonathan Carrivick, Lindsey Nicholson, Jordan Mertes, Rudolf Sailer, and Ivana Stiperski

Spatially and temporally distributed values of glacier aerodynamic roughness (z0) are required to improve estimates of glacier melt. z0, representing the topographically-controlled height above the surface where wind speed reaches zero, is shown by empirical studies to be spatially and temporally dynamic, yet, z0 is commonly overlooked as a tuning parameter in models or generalised between surfaces and over time. Indirect estimates of z0 made from microtopographic measurements allow for rapid data collection over large areas but are sensitive to measurement scale, data resolution and detrending technique. The recent proliferation of remotely sensed topographic data from airborne and satellite sources has created a wealth of resources, as yet untapped in this particular field. We present a multi-scale analysis using data collected from Hintereisferner, Austria, with a view to upscaling current methods for estimating 3D microtopographic z0 so that coarser resolution, broader scale data can be used to estimate z0 at the glacier scale. Our extensive dataset covers a spectrum of scales from 5 x 5 m plots (at sub-cm resolution) to scans of almost the whole glacier surface from an in-situ terrestrial laser scanner.

How to cite: Chambers, J., Smith, M., Smith, T., Quincey, D., Carrivick, J., Nicholson, L., Mertes, J., Sailer, R., and Stiperski, I.: A multi-scale investigation of geometrically derived z0 from Hintereisferner, Austrian Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5581, https://doi.org/10.5194/egusphere-egu2020-5581, 2020.

EGU2020-11547 | Displays | CR2.7

Monitoring isotopic signature in headwaters to trace environmental changes: an example in the Italian Alps

Chiara Marchina, Valeria Lencioni, Francesca Paoli, Marzia Rizzo, and Gianluca Bianchini

Glaciers are shrinking due to global warming, resulting in a diminishing contribution of ice- and snowmelt to headwaters with consequences on freshwater ecosystems. The stable isotopic compositions in natural waters (δ18O and δ2H) respond to environmental variation very sensitively and can indicate the change of geographic environment or mark the recharge of runoff (Boral 2019, Zuecco 2019). Thus, stable isotopes have been used as natural tracers to constrain the contributions of different water sources to streamflow, including snowmelt, icemelt and groundwater baseflow (Boral 2019). Within this context, we tested if water stable isotopes are spatio-temporal tracers of: i) water in periglacial habitats, being the isotopic signature of surface water inherited from the snow/icemelt, groundwater, and rainfall; ii) regional (year-specific) meteorological conditions, being the isotopic signature of precipitations affected by air temperature, humidity and aqueous vapour origin, ascribing stable isotopes in the list of the “essential climate variables″ (ECV). In this light, we investigated the ionic and isotopic composition (δ18O and δ2H) of six high altitude streams and one pond in the Italian Alps (Noce and Sarca basins) during the ablation season in 2018. Differences between habitat types (pond, kryal, rhithral, krenal) were detected. More negative values of δ18O and δ2H were recorded in the kryal and glacio-rhithral sites dominated by ice and snowmelt, in early summer. Less negative values were recorded in these sites in late summer and in krenal sites, dominated by groundwater and rainfall inputs. The isotopic results also showed that the complex alpine orography influences the air masses and moist, ultimately resulting in isotopic differences in precipitations of neighbouring, but distinct catchments (Sarca and Noce basins). As average, less negative values were recorded in the Sarca basin, characterized by a higher contribution of precipitation of Mediterranean origin. Finally, isotopic composition of the entire water population appeared to be strongly influenced by the regional climatic anomaly of the year 2018, which was anomalously warm in respect to the historical series 1961- 1990. This study will provide additional clues for the climate-change debate, proposing water isotopes as “essential climate variables″ indicators for assessing change in a warmer future.

 

Keywords: stable isotopes, glaciers, essential climatic variables

 

References:

Boral S., J. Hydrol., https://doi.org/10.1016/j.jhydrol.2019.123983

Zuecco G., Hydrol. Process, https://doi.org/10.1002/hyp.13366.

How to cite: Marchina, C., Lencioni, V., Paoli, F., Rizzo, M., and Bianchini, G.: Monitoring isotopic signature in headwaters to trace environmental changes: an example in the Italian Alps , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11547, https://doi.org/10.5194/egusphere-egu2020-11547, 2020.

EGU2020-10150 | Displays | CR2.7

Spatially distributed mass balance of 14 Icelandic glaciers, 1945−2017. Trends and link with climate.

Joaquín M. C. Belart, Eyjólfur Magnússon, Etienne Berthier, Águst Þ. Gunnlaugsson, Finnur Pálsson, Guðfinna Aðalgeirsdóttir, Tómas Jóhannesson, and Helgi Björnsson

Excluding the three largest ice caps, Icelandic glaciers have, until recently, received limited attention in terms of mass balance observations over the last century. In this study, mass balance estimates from 1945 to 2017 are presented, in decadal time spans, for 14 glaciers (total area 1054 km2) subject to different climatic forcing in Iceland. The mass balances are derived from airborne and spaceborne stereo imagery and airborne lidar, and correlated with precipitation and air temperature by a first order equation including a reference-surface correction term. This permits statistical modelling of annual mass balances and to temporally homogenize the mass balances for a region-wide, multidecadal mass balance study. The mean (standard deviation) mass balances of the target glaciers were −0.43 (0.17) m w.e. a−1 in 1945−1960, 0.01 (0.21) m w.e. a−1 in 1960−1980, 0.10 (0.23) m w.e. a−1 in 1980−1994, −0.98 (0.44) m w.e. a−1 in 1994−2004, −1.23 (0.57) m w.e. a−1 in 2004−2010 and 0.06 (0.35) m w.e. a−1 in 2010−2017. The majority of mass loss occured in 1994−2010, accounting for 22.5±1.6 Gt (1.4±0.1 Gt a−1). High decadal mass-balance variability is found on glaciers located at the south and west coasts,
in contrast to the glaciers located inland, north and northwest. These patterns are likely explained by the proximity to warm (south and west) versus cold (northwest) oceanic currents.

How to cite: Belart, J. M. C., Magnússon, E., Berthier, E., Gunnlaugsson, Á. Þ., Pálsson, F., Aðalgeirsdóttir, G., Jóhannesson, T., and Björnsson, H.: Spatially distributed mass balance of 14 Icelandic glaciers, 1945−2017. Trends and link with climate., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10150, https://doi.org/10.5194/egusphere-egu2020-10150, 2020.

EGU2020-18706 | Displays | CR2.7

Multi-temporal mass balance changes of the Northern Patagonian Icefield from 1975 to 2016

Etienne Berthier, Ines Dussaillant, Fanny Brun, and Vincent Favier

The northern Patagonian Icefield (NPI) is the second largest ice mass in Patagonia (3740 km²). Estimation of recent volume changes confirm an acceleration of ice loss in the last decades compared to the mean mass loss since the Little Ice Age. However, Icefield-wide responses at shorter time scales (5-25 yrs) are still poorly documented and not well understood.

We compare five digital elevation models (DEM) acquired between 1975 and 2016 over the NPI: SPOT6 and SPOT7 DEMs for year 2016, SPOT5-HRS DEMs for 2012 and 2005, the Shuttle Radar Topography Mission DEM (SRTM) for year 2000 and the earlier Chilean military institute cartography (IGM) derived from aerial photographs acquired in 1975. We derive cefield-wide mass balances during four different time periods (1975-2000, 2000-2005, 2005-2012, 2012-2016). Our results suggest an acceleration of mass loss from 1975 to 2016. Although error bars are large, we suggest a shift from moderately negative icefield-wide mass balance rates before 2000 (of the order of -0.6 m w.e. yr-1), towards larger mass losses during the first decade of the 21st century(of the order of -0.8 m w.e. yr-1) and even more negative value from 2012 to 2016 (-1.2 ± 0.2 m w.e. yr-1).

But these results must be considered cautiously. The 1975-2000 map of elevation change shows a thickening rate of over 1 m/yr which are not supported by image analysis. We stress the need to construct a revised 1975 NPI topography in order to document the NPI mass balance observations back to 1975 with improved confidence.

How to cite: Berthier, E., Dussaillant, I., Brun, F., and Favier, V.: Multi-temporal mass balance changes of the Northern Patagonian Icefield from 1975 to 2016, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18706, https://doi.org/10.5194/egusphere-egu2020-18706, 2020.

EGU2020-11388 | Displays | CR2.7

Morphological and ice dynamic changes induced by the formation of proglacial lakes in Exploradores Glacier, Patagonia.

Inigo Irarrazaval Bustos, Alejandro Dussaillant, Pablo Iribarren Anacona, Sebastián Vivero, Jorge O'Kuinghtton, and Gregoire Mariethoz

Glacier dynamics are sensitive to the formation and expansion of proglacial lakes. Proglacial lakes development can accelerate glacier retreat rate by flotation of the terminus, formation of a calving front, and increased ice flow. Understanding the impacts of proglacial lakes formation and development, which are reported to be growing in number in Patagonia and other regions, is relevant to improve the understanding and prediction of glacier response to climate change.

This study aims to characterize and monitor recent spatial and temporal changes in the lower section of the Exploradores Glacier (15 km2), located at the northeast section of the Northern Patagonian Icefield. A proglacial lake located at the east margin has been expanding by calving since the early 2000s, and supraglacial ponds located at the front of the glacier could coalesce to form a larger proglacial lake.

We performed repeated unmanned aerial vehicle (UAV) surveys to obtain a series of high-resolution orthoimages (10cm/pixel) and digital elevation models (DEM) of the lower section of Exploradores Glacier. The series consists in 7 orthoimages and DEMs across one year (March 2019 to March 2020), forming in a dataset that is the first of its kind for a Patagonian glacier. The images are processed by photogrammetric technique structure from motion using Pix4D software, and are co-registered using stable off glacier tie-points. Next, the orthoimages are correlated using a feature tracking algorithm (IMCORR) to derive glacier flow velocities. Surface lowering and morphological changes is obtained by DEM differencing analysis. In addition, an aerial photographic archive (Aniya et al. 2017) providing a 20-year observation record is incorporated in the analysis. The results of the imagery analysis are compared with in-situ ablation stakes measurement during the summer season 2019-2020, which indicates downwasting rates up to 100mm/day. This allows estimating rates of proglacial lake expansion at the east margin, supraglacial lakes coalescence, and increase in debris-covered area.

This study contributes to a better understanding of the processes that occur during a relatively short period in a highly transient glacier. Future work will include modelling ice dynamics to better characterize and predict the response of the glacier to the development of proglacial lakes.

How to cite: Irarrazaval Bustos, I., Dussaillant, A., Iribarren Anacona, P., Vivero, S., O'Kuinghtton, J., and Mariethoz, G.: Morphological and ice dynamic changes induced by the formation of proglacial lakes in Exploradores Glacier, Patagonia., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11388, https://doi.org/10.5194/egusphere-egu2020-11388, 2020.

EGU2020-13824 | Displays | CR2.7

Glacio-metrological measurements of Patsio glacier, Himachal Pradesh (India), Western Himalaya

Thupstan Angchuk, Allagapan Ramanathan, Arindan Mandal, Mohd Soheb, Somdutta Mishra, and Sarvagya Vatsal

We present the glacio-metrological measurements on the Patsio glacier, located in the Lahaul-Spiti region, Himachal Pradesh, western Himalaya. In-situ annual and seasonal mass balance measurements have been monitored since 2010 and 2012 respectively. Subsequently, an automatic weather station was installed in the summer of 2015. The baseline investigations show a large variability in meteorological conditions during different seasons. Summer was warm and calm, whereas winter is cold and windy with high precipitation, especially snow. Peak ablation months were July and August. Mean annual temperature over the study period was low (-6.3 °C). January recorded as the coldest month and July as hottest corresponding to a mean of -16.8 and 4.28 °C, respectively. Two contrasting wind flow over the Patsio glacier valley was prominent. The persistent katabatic flow was observed during the winter season and up-valley wind in summer. A classic Temperature Index Model was used to estimate the melt from the Patsio glacier, for the years 2016 and 2017. Degree-day factor (DDF) for various components (snow, ice, and debris covered ice) was estimated using field data. High DDFs for snow, ice, and debris-covered ice were observed compared to other studies. The simulated results (snow and ice) were in good agreement with observed data (R2 = 0.88 in 2016 and 0.93 in 2017). Temperature is the main governing factor in inducing the melt. This study gives insight the metrological conditions together with snow and ice melt of Patsio glacier situated in the high and dry region of the Himalaya.

How to cite: Angchuk, T., Ramanathan, A., Mandal, A., Soheb, M., Mishra, S., and Vatsal, S.: Glacio-metrological measurements of Patsio glacier, Himachal Pradesh (India), Western Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13824, https://doi.org/10.5194/egusphere-egu2020-13824, 2020.

EGU2020-17753 | Displays | CR2.7

A field study of mass balance and hydrology of the West Khangri Nup glacier (Khumbu, Everest).

Giovanni Martino Bombelli, Daniele Bocchiola, Federica Camin, and Paolo Maria Ossi

Depiction of glaciers’ dynamics in the high altitudes of Himalaya, and hydrological fluxes therein is often limited, and yet necessary to assess their contribution to overall water budget in the downstream areas. Information about glaciers in these remote regions is often based on satellite data, which routinely document the retreat or advance of ice-covered areas, while volume changes are less easy to quantify, and require local assessment of weather, and hydrology. 
Here, we report investigation of snow accumulation, ice melt, and mass balance of the West Khangri Nup (WKN) glacier (mean altitude 5494 m a.s.l., 0.23 km2), a part of the Khumbu glacier in the Everest region. The glaciers of the area have experienced negative mass balances in the last three decades, and accordingly investigation of their recent, and prospective dynamics seems necessary. 
Weather, glaciological, snow pits, hydrologic, and isotopic data gathered during some field campaigns (2010-2014) on the glacier, and at the EVK2CNR pyramid site are used here to set up the Poli-Hydro glacio-hydrological model, to depict ice and snow melt and hydrological flows, and investigate seasonal snow dynamics on this high region of the glacier.   
Coupling ice ablation data, and Poli-Hydro simulation for ca. 5 years (January 2010-June 2014), we estimated that WKN depleted ca. -10.46 m of ice water equivalent IWE (i.e. annually ca. -2.32 m IWEy-1). Using then snowpack density, and isotopic (δ18O) profiles on the WKN, we demonstrate that local snowpack during field surveys was recent (Fall-Winter 2013-2014), and that significant snow accumulation did not occur recently. Analysis of recent snow cover from LANDSAT images also confirms snow dynamics as depicted. 
We present original data and results, and complement present studies covering glaciers’ mass balance, and investigation of accumulation zones in the Everest region, and the Himalayas, also potentially helpful in the assessment of future dynamics under ongoing climate change.     

How to cite: Bombelli, G. M., Bocchiola, D., Camin, F., and Ossi, P. M.: A field study of mass balance and hydrology of the West Khangri Nup glacier (Khumbu, Everest)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17753, https://doi.org/10.5194/egusphere-egu2020-17753, 2020.

CR3.1 – Risks from a changing cryosphere

Despite the widespread need to use sea-level rise information in coastal adaptation decision making, the production of this information rarely starts from a decision making perspective. This constitutes a major gap, because the specific sea-level information needed for adaptation depends on the type of decision a coastal decision maker is facing. Recent work developed in the context of the World ClimateResearchProgram (WCRP) Grand Challenge “Regional Sea-Level Change and Coastal Impacts” and the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) of the Intergovernmental Panel on Climate Change (IPCC) has started to address this gap by drawing upon the decision analysis literature. This paper presents this work identifying what kind of mean sea-level rise (SLR) information is needed for local coastal adaptation decisions. A special emphasis is placed on the contributions of the melting of the ice sheets of Greenland and Antarctica to global mean SLR, as these processes may contribute significantly to future SLR and, at the same time, are most uncertain. First, different types of coastal adaptation decisions are characterized in terms of decision horizons and users' uncertaintytolerance. Next, suitable decision analysis approaches and sea-level information required for these are identified. Finally it is discussed if and how these information needs can be met given the state-of-the-art of sea-level science. It is found that four types of information are needed: i) probabilistic predictions for short term decisions when users are uncertainty tolerant; ii) high-end and low-end SLR scenarios chosen for different levels of uncertainty tolerance; iii) upper bounds of SLR for users with a low uncertainty tolerance; and iv) learning scenarios derived from estimating what knowledge will plausibly emerge about SLR over time. Probabilistic predictions can only be attained for the near term (i.e., 2030-2050) and for locations for which modes of climate variability are well understood and the vertical land movement contribution to local sea-levels is small. Meaningful SLR upper bounds cannot be defined unambiguously from a physical perspective. Low to high-end scenarios for different levels of uncertainty tolerance, and learning scenarios can be produced, but this involves both expert and user judgments. The decision analysis procedure elaborated here can be applied to other types of climate information that are required for adaptation purposes.

How to cite: Hinkel, J.: Generating sea-level information for coastal adaptation: a risk management perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4989, https://doi.org/10.5194/egusphere-egu2020-4989, 2020.

EGU2020-8408 | Displays | CR3.1 | Highlight

Degrading permafrost threatens Arctic nature and built environment

Jan Hjort, Olli Karjalainen, Juha Aalto, Sebastian Westermann, Vladimir Romanovsky, Frederick Nelson, Bernd Etzelmüller, and Miska Luoto

Arctic earth surface systems are undergoing unprecedented changes, with permafrost thaw as one of the most striking examples. Permafrost is critical because it controls ecosystem processes, human activities, and landscape dynamics in the north. Degradation (i.e. warming and thawing) of permafrost is related to several hazards, which may pose a serious risk to humans and the environment. Thaw of ice-rich permafrost increases ground instability, landslides, and infrastructure damages. Degrading permafrost may lead to the release of significant amounts of greenhouse gases to the atmosphere and threatens also biodiversity, geodiversity and ecosystem services. Thawing permafrost may even jeopardize human health. Consequently, a deeper understanding of the hazards and risks related to the degradation of permafrost is fundamental for science and society.

To address climate change effects on infrastructure and human activities, we (i) mapped circumpolar permafrost hazard areas and (ii) quantified critical engineering structures and population at risk by mid-century. We used observations of ground thermal regime, geospatial environmental data, and statistically-based ensemble methods to model the current and future near-surface permafrost extent at ca. 1 km resolution. Using the forecasts of ground temperatures, a consensus of three geohazard indices, and geospatial data we quantified the amount and proportion of infrastructure elements and population at risk owing to climate change. We show that ca. 70% of current infrastructure and population in the permafrost domain are in areas with high potential for thaw of near-surface permafrost by 2050. One-third of fundamental infrastructure is located in high hazard regions where the ground is susceptible to thaw-related ground instability. Owing to the observed data-related and methodological limitations we call for improvements in the circumpolar hazard mappings and infrastructure risk assessments.

To successfully manage climate change impacts and support sustainable development in the Arctic, it is critical to (i) produce high-resolution geospatial datasets of ground conditions (e.g., content of organic material and ground ice), (ii) develop further high-resolution permafrost modelling, (iii) comprehensively map permafrost degradation-related hazards, and (iv) quantify the amount and economic value of infrastructure and natural resources at risk across the circumpolar permafrost area.

How to cite: Hjort, J., Karjalainen, O., Aalto, J., Westermann, S., Romanovsky, V., Nelson, F., Etzelmüller, B., and Luoto, M.: Degrading permafrost threatens Arctic nature and built environment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8408, https://doi.org/10.5194/egusphere-egu2020-8408, 2020.

EGU2020-11374 | Displays | CR3.1

14 years of LiDAR monitoring and insights into ice of rockwall permafrost: the east face of the Tour Ronde (3792 m, Mont Blanc massif)

Alexandre Lhosmot, Ludovic Ravanel, Suzanne Preunkert, Florence Magnin, Grégoire Guillet, Antoine Rabatel, and Philip Deline

The increasing rockfall frequency in high mountain rockwalls is generally associated with global warming via the permafrost warming but long series of high resolution data on rockfall are still necessary to better appreciate the evolution of their frequencies and volumes, and to better understand their triggering factors.

Here we present an inventory of rockfalls surveyed by terrestrial laser scanning (LiDAR) since 2005 in the east face of the Tour Ronde (3792 m a.s.l.) in the Géant glacial basin (Mont Blanc massif).

Between 2005 and 2018, the rockwall was scanned 12 times, giving 11 comparisons of 3D models [1]. These highlighted a very intense morphodynamics with 91 destabilizations with volumes between 1 and 15,578 m3 for a total volume of 31,610 m3 (mean erosion rate: 29,8 mm.yr-1). In the first year of measurement, the Bernezat spur was affected by a collapse of more than 700 m3 [2]. Then, it was affected by rockfalls not exceeding a few tens of m3. On the other hand, in the rest of the face, there is a very strong increase in rockfall activity, especially during the hot summer 2015 at the end of which (August 27) the most voluminous collapse of the whole period occurred.

The modelled surface temperature distribution at the scale of the Mont Blanc massif [3] attests to the presence of permafrost throughout the rockslope, confirmed by temperature measurements carried out at 3, 30 and 55 cm deep in the rock at the base of the Bernezat spur between October 2006 and May 2009. In addition, the main collapses left massive ice, at the level of their scar, more or less mixed with rock debris. These different elements, associated with the fact that collapses occur essentially during and following the highest summer heat, point to the role of degradation of permafrost [4]. A collapse on December 4, 2018 at the level of the small spur located at the foot of the Bernezat and whose volume is estimated at 7000 m3 reinforces this hypothesis since the detachment surface was covered - except for its margins - by massive ice. This has been sampled and its dating will perhaps confirm the age of the ice present in the cracks of the permafrost-affected rockwalls of the Mont Blanc massif. In 2017, a collapse of 44,000 m3 in the north face of the Aiguille du Midi (3842 m a.s.l.) had exposed 4060 calBP ice. In the Tour Ronde case, ice/snow cover changes and glacial debutressing could also partly explain the rockfall activity.

 

 

[1] Ravanel L. et al. (2010). Revue Française de Photogrammétrie et de Télédétection, 192 : 58-65.

[2] Rabatel A. et al. (2008). Geophysical Research Letters, 35: L10502.

[3] Magnin F. et al. (2015). Geomorphologie, 21: 145-162.

[4] Ravanel L. et al. (2017). Science of the Total Environment, 609: 132-143.

How to cite: Lhosmot, A., Ravanel, L., Preunkert, S., Magnin, F., Guillet, G., Rabatel, A., and Deline, P.: 14 years of LiDAR monitoring and insights into ice of rockwall permafrost: the east face of the Tour Ronde (3792 m, Mont Blanc massif), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11374, https://doi.org/10.5194/egusphere-egu2020-11374, 2020.

EGU2020-8236 | Displays | CR3.1

Experimental microfracture propagation in gneiss through frost wedging

Flavio Anselmetti, Ferdinando Musso Piantelli, Marco Herwegh, Marius Waldvogel, and Ueli Gruner

Ice-driven mechanical weathering in mountainous environment is considered an efficient process for slow preconditioning of rockfalls. In this study (Musso Piantelli et al., 2020), we simulate with an innovative experimental approach subcritical fracture-propagation under frost-wedging conditions through pre-existing weaknesses of intact rock bridges. Two series of freeze-thaw experiments in an environmental chamber have been designed to investigate and monitor the propagation of artificially-induced fractures (AIF) in two twin gneiss samples. By employing 3D X-Ray Computed Tomography and a displacement sensor, an accurate characterization and new insights into the fracture-propagation mechanism are provided. Our results demonstrate that frost wedging propagated the AIFs of 1.25 cm2 and 3.5 cm2 after 42 and 87 freeze-thaw cycles, respectively. The experiments show that volumetric expansion of water upon freezing, cooperating with volumetric thermal expansion and contraction of the rock, plays a key role in fracture widening and propagation. Based on these results, this study proposes that: (i) frost wedging exploits intrinsic pre-existing weaknesses of the rock; (ii) the fracturing process is not continuous but alternates propagation stages to phases of tensile stress accumulation; and (iii) downward migration of “wedging grains”, stuck between the walls of the fracture, increases the tensile stress at the tip, widening and propagating the fractures with each freeze-thaw cycle. The experimental design developed in this study offers the chance to visualize fracture-propagation in natural joints quantifying the long-term efficiency of this process in near-natural scenarios.

REFERENCES

Musso Piantelli, F., Herwegh, M., Anselmetti, F.S., Waldvogel, M., Gruner, U., (2020). Microfracture propagation in gneiss through frost wedging: insights from an experimental study. Natural Hazards, 1-18. https://doi.org/10.1007/s11069-019-03846-3

How to cite: Anselmetti, F., Musso Piantelli, F., Herwegh, M., Waldvogel, M., and Gruner, U.: Experimental microfracture propagation in gneiss through frost wedging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8236, https://doi.org/10.5194/egusphere-egu2020-8236, 2020.

EGU2020-9717 | Displays | CR3.1

Ice avalanche risk management from the Planpincieux glacier (Courmayeur - Italy)

Paolo Perret, Fabrizio Troilo, Simone Gottardelli, Luca Mondardini, Niccolò Dematteis, Daniele Giordan, and Valerio Segor

Instabilities occurring on temperate glaciers in the Alps have been the subject of several studies, which have highlighted preliminary conditions and possible precursory signs of break-off events.

Since 2013, the Planpincieux Glacier, located on the Italian side of Mont Blanc massif (Aosta Valley), has been studied to analyse the dynamics of ice collapses in a temperate glacier.

These analyses have been conducted for several years, enabling the assessment of surface kinematics on the lower glacier portion and the different instability processes at the glacier terminus. During the period of the study, especially in the summer seasons, increases in velocities of the whole right side of the glacier tongue have been recorded. This fast sliding movement is mainly induced by water flow at the bottom of the glacier.

In 2019 summer season, the increase of speed coincided with the opening of a large crevasse, which outlined a fast moving ice volume, assessed by photogrammetric techniques as 250.000 m3.

According to the risk scenarios, the collapse of this ice volume from the glacial body would have reached the valley floor, potentially affecting the access road to the Val Ferret valley.

Considering the potential risk, a civil protection plan has been deployed by the monitoring team of the Aosta Valley Autonomous Region, Fondazione Montagna sicura and CNR-IRPI.

Glacier displacements, variations in the glacier morphology and environmental variables, such as air temperature, rain and snowfall, have all been taken into account to implement the monitoring plan.

This work outlines and summarises the steps used to develop the scientific knowledge into an integrated monitoring plan and a closure plan for the Val Ferret valley.

How to cite: Perret, P., Troilo, F., Gottardelli, S., Mondardini, L., Dematteis, N., Giordan, D., and Segor, V.: Ice avalanche risk management from the Planpincieux glacier (Courmayeur - Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9717, https://doi.org/10.5194/egusphere-egu2020-9717, 2020.

In recent years, the number and size of glacial lakes in mountain regions have increased worldwide associated to the climate-induced glacier retreat and thinning. Glacial lakes can cause glacial lake outburst floods (GLOFs) which can pose a significant natural hazard in mountainous areas and can cause loss of human life as well as damage to infrastructure and property.

The glacial landscape of the Jostedalsbreen ice cap in south-western Norway is currently undergoing significant changes reflected by progressing glacier length changes of the outlet glaciers and the formation of new glacial lakes within the recently exposed glacier forefields. We present a new glacier area outline for the entire Jostedalsbreen ice cap and the first detailed inventory of glacial lakes which were formed within the newly exposed ice-free area at the Jostedalsbreen ice cap. In detail, we explore (i) the glacial lake characteristics and types and (ii) analyse their spatial distribution and hazard potential.

For the period from 1952-1985 to 2017/2018 the entire glacier area of the Jostdalsbreen ice cap experienced a loss of 79 km2. A glacier area reduction of 10 km2 occurred since 1999-2006. Two percent of the recently exposed surface area (since 1952-1985) is currently covered with newly developed glacial lakes corresponding to a total number of 57 lakes. In addition, eleven lakes that already existed have enlarged in size. Four types of glacial lakes are identified including bedrock-dammed, bedrock- and moraine-dammed, moraine-dammed and ice-dammed lakes. Especially ice- or moraine-dammed glacial lakes can be the source of potentially catastrophic glacier lake outburst floods. According to the inventory of glacier-related hazardous events in Norway GLOFs represent the most common hazardous events besides ice avalanches and incidents related to glacier length changes. Around the Jostedalsbreen ice cap several historical but also recent events are documented. The majority of the events caused partly severe damage to farmland and infrastructure but fortunately no people have been harmed by today.

Due to the predicted increase in summer temperatures for western Norway until the end of this century, it is very likely that the current trend of an accelerated mass loss of Norwegian glaciers will continue. As one consequence of this development, further new lakes will emerge within the newly exposed terrain. The development of new glacial lakes has diverse regional and global socio-economic implications. Especially in mainland Norway, where glaciers and glacier-fed streams have a high importance for hydropower production, tourism and climate research it is essential to gain a better understanding of the possible impacts of glacial lakes for being prepared for risks but also advantages arising from these newly emerging landscape elements.

How to cite: Laute, K. and Beylich, A. A.: The formation of new glacial lakes at the Jostedalsbreen ice cap in southwest Norway and their future implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5012, https://doi.org/10.5194/egusphere-egu2020-5012, 2020.

EGU2020-12399 | Displays | CR3.1

A national inventory of potential future lakes in the deglaciating cordilleras of Peru for integrative water and risk management

Lucía Guardamino, Fabian Drenkhan, Wilfried Haeberli, Randy Muñoz, and Alejo Cochachin

Anticipating the formation of lakes in deglaciating mountains represents an important step towards the identification of both, new possible water storage options and potential hazards. This is particularly crucial in the Peruvian Andes which are characterized by strong precipitation seasonality. Dwindling glacier contribution to river streamflow, particularly during the dry season (May-September), combined with increasing water demand suggest considerable levels of potential future water scarcity in some regions. Within the near future, the water use potential of new lakes needs to be further explored for main sectors of water use. At the same time, emerging risks must be considered for downstream populations (i.e. lakes increasingly exposed to landslides, avalanches, rock falls or ice detachments).

In this context, the presented future lakes inventory aims to provide information for long-term planning and comprehensive territorial management. The methodology is based on numerical ice thickness distribution (±30% uncertainty range) and bedrock modelling with the GlabTop (Glacier bed Topography) model. This tool in combination with a visual inspection protocol based on geomorphological criteria allows for reasonable estimates and evaluation of potential future lakes differentiated by confidence levels. The three applied morphological criteria were: i) downslope (priority) and upslope increase of surface slope, ii) lateral glacier narrowing, and iii) heavily crevassed areas following a crevasse-free zone. The results are most robust for the identification of potential formation sites rather than the precise area, depth or volume of potential lakes. Thus, the inventory needs to be understood as a first order of magnitude.

A total of 287 sites of potential future lakes (>1ha) have been identified which would be distributed within 11 out of 18 still glacier-covered mountain ranges in Peru. The total lake volume would be about 231 millions of m³ which corresponds to around 0.5-1.0% of the entire estimated national glacier volume (~38 km³). While on a country scale this might not be much, locally the projected water storage could play an important role. Actually, a major number (175) of the identified lakes has already developed or is likely to form within a few decades. This underlines the need for more research and integrated territorial management within a timely manner.

The current methodology and compiled inventory provide an important tool for prospective and integrated risk, water and land management within a context of hydroclimatic and socioeconomic impacts in the Andes of Peru and elsewhere. Follow-up studies should use new data and additional methods including in-situ techniques to corroborate and update results within a rapidly changing Andean environment. Additionally, a realistic and detailed evaluation should be particularly conducted for possible lakes of higher priority concerning water supply and outburst flood susceptibility.

How to cite: Guardamino, L., Drenkhan, F., Haeberli, W., Muñoz, R., and Cochachin, A.: A national inventory of potential future lakes in the deglaciating cordilleras of Peru for integrative water and risk management, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12399, https://doi.org/10.5194/egusphere-egu2020-12399, 2020.

Mountain glacier is an indispensable supplier and modulator of freshwater to human’s sustenance in extensive cold and arid areas of the world. Melt waters from glaciers are widely used for ecosystem integrity, agricultural irrigation, hydropower operation, domestic and industrial activities. Under the background of global environmental changes such as global warming and regional population growth, linking climate-related glacio-hydrological changes to regional population growth is of the essence. However, a global assessment on opportunities/risks caused by glacial meltwater changes and population growth has not been presented until now. In this study, the population changes in glacier-fed area (GFA) for historical (1980-2015) and future (2010-2100) periods at the global, continental, national and basin scales were first mapped. Then, the opportunities/risks associated with population growth and glacier meltwater changes during 1980-2100 in 42 large-scale glacierized drainage basins with a minimum population of 10 thousand in 2015 were analyzed. Results reveal that the population living in the world’s GFA was 2030 million in 2015 and it was rapidly increased from 1278 million in 1980. The total population in GFA would continue to increase until a maximum is reached (e.g. peak population will appear around 2060 under the intermediate pathway for mitigation and adaptation, i.e. SSP2), beyond which the population would gradually decline. The opportunities/risks vary across basins and decades. Both of them are greatest in the Indus River basin, where the increase in glacial meltwater can seasonally satisfy the basic needs of additional 87 million people from the 2000s to 2040s, but about 200 million would be exposed to severe water scarcity due to the decrease in glacial meltwater and the population increase after the 2040s. 

How to cite: Su, B., Xiao, C., and Chen, D.: Opportunities & risks associated with global glacial meltwater changes and regional population growth from 1980 to 2100, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3853, https://doi.org/10.5194/egusphere-egu2020-3853, 2020.

EGU2020-4110 | Displays | CR3.1

Geomorphic signatures of large-scale glacier detachments

Mylène Jacquemart, Matthias Leopold, Ethan Welty, Lia Lajoie, Michael Loso, and Kristy Tiampo

The catastrophic detachment of Kolka Glacier in Russia was long thought to be a unique occurrence (e.g., Haeberli et al., 2004), but recent events in Tibet, Alaska, Argentina and China have increased the urgency to understand these processes and the risk they pose to mountain communities and infrastructure. Most notably, the tongues of two neighboring glaciers in Tibet detached only a few weeks apart in 2016, the first killing nine herders and hundreds of their livestock. In 2013 and 2015 Flat Creek Glacier in Alaska’s Saint Elias Mountains lost half of its total area in two large detachments. The resulting destructive mass flows left a clear scar in the landscape, piling debris up to 30 m thick and spreading it over 8 km2. Recent investigations by Kääb et al. (2018), Gilbert et al. (2018) and Jacquemart et al. (in review) suggest that the failures in Tibet and Alaska share three main drivers: temperate ice restricted by a frozen glacier tongue, a clay-rich bed, and increased meltwater input to the base of the glacier, driven by increasing summer temperatures.

Here we ask whether these glacier detachments are indeed a new, emerging hazard or whether we simply have not previously recognized the signs they leave in the landscape. Only a long-term record of observations stretching beyond the modern satellite era, can reliably answer the question about possibly increasing frequencies. In order to start building some understanding of the nature of such deposits, we investigated the internal structure and landscape setting of the 2013 and 2015 detachment deposits at Flat Creek. We performed electrical resistivity tomography surveys to estimate their ice content and ice distribution. In addition we analyzed grain size distributions and orientations in the deposits to see if they can be clearly distinguished from other glacio-fluvial deposits. To understand if glacier detachments have happened in this region before, we performed the same analysis on large debris deposits found downstream of a neighboring glacier. We combine this field evidence with remote sensing analysis of the temporal evolution of the glaciers and detachment deposits in Alaska, Tibet and Russia to understand the signatures of these catastrophic events in the landscape. Our preliminary results for Alaska show that the glacier itself is a bad indicator of past events, as the ice response quickly masks the detachment. Additionally, we found ice in the deposits to be highly broken up and ground, though never the less able to endure multiple years. Unlike a traditional debris-flow deposits, the glacier-detachment deposits exhibit a lack of grain-size sorting, and the grain orientations appear highly chaotic, with a tendency toward vertical orientations. As such, the deposits appear clearly distinct from the surrounding hillslope, and further analysis will show to what extent they can be distinguished from other glacio-fluvial deposits.

How to cite: Jacquemart, M., Leopold, M., Welty, E., Lajoie, L., Loso, M., and Tiampo, K.: Geomorphic signatures of large-scale glacier detachments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4110, https://doi.org/10.5194/egusphere-egu2020-4110, 2020.

EGU2020-4442 | Displays | CR3.1

Distribution and morpho-thermal characteristics of rock glaciers in southern Peru: case, Cordilleras Huanzo and Chila

Katy Medina, Edwin Loarte, Edwin Badillo, Hairo Leon, Francisco Castillo, and Christian Huggel

Climate change generates significant impacts on high mountain regions, especially considering the sensitivity of tropical glaciers. However, information about rock glaciers are very scarce and there is very limited research in this field in Peru. Rock glacier concentrate mainly in the southern part of Peru where 95% of rock glaciers are located. Here we present for the first time an overview of rock glacier occurrence and characteristics in Peru.

The Cordilleras Huanzo and Chila are located in the mountain ranges in the southern region of Peru, Huanzo in the administrative region of Apurimac, Arequipa, Cusco and Ayacucho, while Chila in Arequipa. Both cordilleras extend from S 15°39'41.36" to 14°03'17.54" and W 73°24'12.55" to 71°27'113.20". For this study, remote sensing tools and geographic information system were applied, using images from Google Earth-Pro and SASPlanet, corrected DEM ALOS Palsar (12.5m), MERIT DEM (90m) and WorldClim data (1970-2000) 1 km2.

The results indicate that in the cordillera Huanzo there are 317 rock glaciers with a total area of 26.97 km2 and in the cordillera Chila there are 289 rock glaciers with 17.96 km2. Concerning their activity or dynamic there are 295 intact (active and inactive) rock glaciers and 311 relict or fossil rock glaciers.

The results further indicate that rock glaciers are located in thermal ranges between -1.53°C and 3.97°C. The relict or fossil types are located in the thermal range between -1.34°C and 3.97°C, while intact types between -1.53°C and 2.56°C. The rock glaciers of the cordillera Huanzo are located at an average altitude of 4497 to 5221 m.a.s.l., while in the cordillera Chila at 4470 to 5454 m.a.s.l. The aspect is predominantly S to SW.

Rock glaciers contain ice which may represent a potential water reserve in arid regions in Southern of Peru. The greatest distribution of these resources is found in the Camana and Ocoña basins of the Pacific watershed with 38.1 km2 of rock glacier area. In the Atlantic watershed, 6.8 km2 of rock glaciers are located in the Alto Apurimac and Ocoña basins.

How to cite: Medina, K., Loarte, E., Badillo, E., Leon, H., Castillo, F., and Huggel, C.: Distribution and morpho-thermal characteristics of rock glaciers in southern Peru: case, Cordilleras Huanzo and Chila, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4442, https://doi.org/10.5194/egusphere-egu2020-4442, 2020.

EGU2020-4452 | Displays | CR3.1

Variation of glacial dynamics in Peru: from valley glaciers to mountain glaciers in a context of climate change

Edwin Loarte, Katy Medina, Yadira Curo, Hairo Leon, Fiorella Quiñonez, Francisco Castillo, and Christian Huggel

One of the effects of climate change on tropical glaciers is the accelerated reduction of their glacial tongue, reflected in a morphometric variation. Many glaciers that had pronounced tongues and that extended through a valley (Valley glacier) now have reduced their fronts located in the upper parts of the valleys (Mountain glacier).

This has been studied with glaciers of Peru located in 18 mountain ranges located from S 8°20'56" to 15°53'26" and W 77°56'10" to 69°05'14", which are an important solid water reserve that directly supplies the population of 11 departments.

The study focused on the "digit 1" (primary classification) of the Global Land Ice Measurement from Space (GLIMS), which classifies the glaciers mainly in: valley glaciers and mountain glaciers. The processing of raster and vector data through the use of geographic information system and remote sensing tools allowed to analyze the changes and variations affecting glaciers with respect to their morphometry. For this, a comparison was made between glacier coverage in 2016 (using images Sentinel 2), produced by INAIGEM, and the baseline of the glacier coverage of 1955 and 1970 (using aerial photography), from the first inventory of glaciers in Peru, produced by Hidrandina S.A.

The results show a significant morphometric variation of 83.7%, where valley glaciers (from Hidrandina inventory) became mainly mountain glaciers. Nowadays only four mountain ranges have mountain glaciers inside whereas in the past it were nine. When we analyze the results for watersheds, the most morphometric changes were 89% in the Atlantic watershed, followed by 57% in the Pacific watershed; in the Amazon watershed there was not any registration of any mountain glaciers since the first inventory in Peru. The surface changes do not show specific any predominant aspect, and average slopes are between 25° and 50°.

The glacial tongues that are considered valley glacier area located in ablation zones, where the mass balance is negative and there is more susceptibility to reducing their mass and, consequently, to variations in shape and size in a short period. This change has been accentuated in recent decades.

How to cite: Loarte, E., Medina, K., Curo, Y., Leon, H., Quiñonez, F., Castillo, F., and Huggel, C.: Variation of glacial dynamics in Peru: from valley glaciers to mountain glaciers in a context of climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4452, https://doi.org/10.5194/egusphere-egu2020-4452, 2020.

With the climate warming, high mountainous areas, including cryosphere, show more frequent and early outbreaks trend in flood hazard, cursing more losses to downstream areas. Based on meteorological, hydrological and MODIS snow cover data, using the snowmelt runoff model (SRM) to simulate and verify the spring runoff result during the snowmelt period from 1990 to 2012 in the upper Heihe River. SRM model simulates results shows it has a high accuracy (NSE = 0.7229), which can be used to predict the future flood intensity changes in studying area. In order to predict the trends of Heihe River Basin in flood return periods under the different future climate change scenarios, analyze used the temperature and precipitation forecast data. By the end of this century, the result of flood runoff shows differently according to climate change scenarios compared with the basic period. In RCP 2.6, due to the small changes of the temperature and precipitation, flood intensity will change slightly around 10% in all return periods; in RCP 4.5, it will increase about 20%; in RCP 8.5, return periods may be rise over 30%.

How to cite: Zhu, G.: Spring Snowmelt Flood Estimate in the Upper Heihe River under Climate Change Scenarios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4604, https://doi.org/10.5194/egusphere-egu2020-4604, 2020.

EGU2020-5454 | Displays | CR3.1

Analysis of the Miage Glacier Lake GLOFs (Aosta Valley - Italy).

Fabrizio Troilo, Valerio Segor, Paolo Perret, Manuel Bertholin, Luca Mondardini, and Simone Gottardelli

Miage Glacier Lake is a glacial marginal lake that forms on the right snout of Miage Glacier, located in the Val Veny Valley (Aosta Valley – Italy). The lake has been experiencing seasonal drainages at least since the 1930’s and 15 events have been documented from 1930 to 1990. The lake position has been almost unvaried since the first existing maps of late 1700, but lake morphology experienced major changes after the drainage event of September 2004, after which the water level could not reach again a sufficient height to fill the 3 depressions that used to form a bigger lake until 2003 (36.000 m2). The lake having decreased its volume and surface, it did not seem by that time that GLOF from Miage Lake could cause any risk downstream (Deline et Al. 2004), but recent observation of Sentinel 2B satellite images  led to the individuation of unusual lake expansion towards its north shore. Thus, an UAV survey was performed to assess the actual lake area in July 2019, and the integration of satellite images and UAV surveys demonstrated a consistent lake area expansion since 2015. Moreover an emptying occurred in late August 2019 so that another UAV survey could be performed, and water volume estimation could be performed by means of DEM differencing. An important water volume was individuated, reaching 196.000 m3 and an estimation of maximum subglacial GLOF debit has been performed. Global evolution trend of the glacier mass has been evaluated by analyzing different airborne Lidar surveys (1991-2008). A cumulated geodetic mass balance could be thus inferred and found good matching with remote sensed analysis (2003-2012) performed by means of stereo satellite imagery by Berthier et Al. in 2014. Average surface lowering of the glacier surface could be analyzed and average values of -1.12 m/yr could be observed around lake Miage. The strong elevation loss of Miage Glacier lower snout is probably the cause of the lowering of the piezometric level in intra-glacial water limiting maximum altitude that water level can reach in the lake, so that the bigger basin of 2004 cannot be filled anymore. Moreover, an analysis of recent GLOFs of Miage Lake gave an insight about the possible dynamics of lake subglacial drainage, suggesting the existence of 2 different mechanisms of emptying as some events occur with lower water debits, earlier in the season, and other events occur later in the summer season with major water debits. Similar GLOF behavior has been described at Plaine Morte Glacier Lake in the Canton of Bern-Switzerland (Fahrni 2018). Field surveys of 2018 showed very likely evidence of hydrostatic uplift of the ice dam, so multi temporal UAV surveys and GNSS field surveys are planned for 2020 to possibly highlight evidences of hydrostatic uplift of the glacier prior to GLOFs.

How to cite: Troilo, F., Segor, V., Perret, P., Bertholin, M., Mondardini, L., and Gottardelli, S.: Analysis of the Miage Glacier Lake GLOFs (Aosta Valley - Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5454, https://doi.org/10.5194/egusphere-egu2020-5454, 2020.

EGU2020-5945 | Displays | CR3.1

A Rockfall inventory: Ötztal Alps, Tyrol, Austria

Bettina Knoflach, Hannah Tussetschläger, Rudolf Sailer, Gertraud Meißl, and Johann Stötter

Climate change has serious implications for the cryosphere and a close relationship between the instability of rock faces and the changes in high mountain permafrost is suspected. Although, the number of rockfall events in Alpine areas is increasing, detailed analyses of the frequency and runout distances in high altitudes are rare. This study gives an insight into the rockfall activity in the Ötztal Alps in Tyrol, Austria. A systematic observation utilizing bi-temporal ALS-DTMs in combination with orthoimages revealed a total of 93 rockfalls over an area of 637 km² in the period from 2006 to 2010. Since more than 90 % of the rockfall release areas were mapped in potential permafrost areas, a correlation between rockfall activity and climatically driven degradation of permafrost in bedrock is very likely. 18 rockfall events, ranging in volume from 69 to 8420 m³, were suitable for runout assessments. To estimate the maximum range of future rockfalls with empirical models, values of 30 ° (Fahrböschung) and 26 ° (minimum shadow angle) can be proposed for risk assessment at a regional scale (1:25,000 – 1:100,000). Rockfalls occurring on snow or ice may also go below these values.

Keywords: Rockfall, Permafrost, digital elevation model; runout distance, Fahrböschung, minimum shadow angle, Ötztal Alps

How to cite: Knoflach, B., Tussetschläger, H., Sailer, R., Meißl, G., and Stötter, J.: A Rockfall inventory: Ötztal Alps, Tyrol, Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5945, https://doi.org/10.5194/egusphere-egu2020-5945, 2020.

EGU2020-6471 | Displays | CR3.1

Assessment of glacier lakes development in Central Caucasus

Ivan Lavrentiev, Dmitry Petrakov, Stanislav Kutuzov, and Andrey Smirnov

Glacier mass loss and consequent termini retreat lead to formation and growth of glacier lakes. In the Mt. Elbrus region, outbursts of lakes formed in recent decades have led to human casualties and significant damage. Building codes of Russian Federation on engineering surveys do not regulate the possibility of glacier lake formation in front of retreating glaciers, which can lead to errors in the future engineering design. Using ground based and airborne GPR data, as well as global ice thickness models, we have identified areas of potential lake formation on glacier bed for a number of glaciers in the Mt. Elbrus region. The method was tested by retrospective modeling for Bolshoy Azau and Djikiugankez glaciers bed topography on the base of 1957 topographic map. In the areas where glaciers disappeared by 2017, out of 13 simulated closed bed depressions 7 existing lakes were predicted by the hydraulic potential. 6 closed depressions on Djikiugankez glacier bed as of 1957 are currently absent, which might be related to the model uncertainties and the original DEMs errors, as well as to possible filling of lakes by sediments. Retrospective modeling of the Bashkara glacier bed topography based on SRTM DEM (2000) showed significant growth potential of the lake Lapa. Retrospective modeling of the Kaayarty glacier bed topography has not provided a clear answer about the possibility if subglacial lake outburst flood was a trigger for catastrophic debris flow formation during the summer of 2000.

In case of total disappearance of Bolshoy Azau, Djikiugankez and Bashkara glaciers at least 11 new lakes with total area of about 1.7 km2 and an average depth of 8 m will form. While the deepest lake will appear in ablation zone of Bolshoy Azau glacier (at elevation 3100-3400 m a.s.l.) the largest in area (1 km2) glacial lake will be formed at the Djikiugankez snout with maximum depth of 40 m and mean depth of 7.2 m. The simulation also showed that in the present conditions, glacier bed lakes of different number and size may also exist under studied glaciers. Our estimates may contain uncertainties due to low resolution of airborne GPR data and the lack of GPR data for Kaayarty glacier, DEM and ice thickness model errors. Detailed ground-based radar survey planned for the summer 2020 will enable the assessment of the size and volume of the potential lakes under Bolshoy Azau glacier.

This work was funded by RFBR grant No. 18-05-00520.

How to cite: Lavrentiev, I., Petrakov, D., Kutuzov, S., and Smirnov, A.: Assessment of glacier lakes development in Central Caucasus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6471, https://doi.org/10.5194/egusphere-egu2020-6471, 2020.

Peruvian Cordillera Negra (8°40’ – 10°30’ S; 77°20’ – 78°30’ W) is characterised by dry semi-arid climate and a general lack of water, especially during the dry season (April – October). Numerous glacial lakes – remnants of the past glaciation of this currently glacier ice-free mountain range – thus represent an important water reservoirs. Glacial lakes sustain environmental flows during dry season, store water for grazing animals as well as simple agricultural irrigation. At the same time, climate change and socio-economic development drive increasing pressure on water resources in the region.

To further enhance potential of glacial lakes in water management, hundreds of glacial lakes of the Cordillera Negra have been equiped by damming structures in order to: (i) increase the volume of retained water; (ii) manage the outflow throughout the seasons of the year. Two general types of dams are distinguished: (i) traditional dams (built by local communities from stones, turf and clay); and (ii) modern dams (concrete or embankment earth- or rock-filled). While these dams help to retain water and the idea is promising, the implementation and dam management lag behind.

During the field visit conducted in 2019, many of the visited dams (both traditional and modern) were documented to leak through; attempts to retain as much water as possible also led to the intentional blocking of spillways, reducing dam freeboard to only tens of cm in some cases. In the worst case, these unacceptable management practices might result in dam overtopping or dam failure. Despite the uppermost part of the Cordillera Negra is not densely settled, some of the glacial lakes are located upstream mining areas, so that there is a risk of environmental pollution and contamination in case of flood. These observations suggest that glacial lakes can successfully be used in water mangement, however, they need to be managed properly and continuously.

How to cite: Emmer, A.: Enhancing water management by using glacial lakes: examples of opportunities and risks from deglaciated Cordillera Negra, Peru, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8631, https://doi.org/10.5194/egusphere-egu2020-8631, 2020.

EGU2020-8972 | Displays | CR3.1

Long-term coupled permafrost-groundwater interactions at Olkiluoto, Finland

Denis Cohen, Thomas Zwinger, Lasse Koskinen, and Tuomo Karvonen

Understanding permafrost development and its effect on groundwater flow patterns and fluxes in the event of future ice-age conditions is important for the long-term safety of spent nuclear fuel repositories. To assess the evolution of permafrost thickness, talik development, and groundwater flow and salinity changes at Olkiluoto, Finland, during the next 100,000 years, we solve Darcy flow coupled to heat and solute transport in three dimensions in a rectangular block representing an area of 8.8 km by 6.8 km, and down to a depth of 10 km. The set of equations is based on continuum thermo-mechanic principles. Important and highly non-linear coupling processes such as the exponential decrease of permeability with ice content in soils and rocks, solute rejection during freezing, and variable-density Darcy flow are fully taken into account. Model equations are solved using the finite element method implemented in the open source software Elmer.  High-resolution data of rock and soil permeability, thermal and physical properties, are mapped onto a 30-meter resolution grid resulting in a system of about 5 million nodes and 5 million elements. Soil layers at the surface are vertically resolved down to 0.1 meter. High contrast in permeability over short distances (from soil to granitic bedrock) make the system of equations challenging to solve numerically. Simulations are driven by RCP 4.5 climate scenario that predicts cold periods between AD 47,000 and AD 110,000. Surface boundary condition for temperature is calculated based on freezing and thawing n-factors that depend on monthly temperatures and the topographic wetness index that defines different zones of vegetation and ground cover. The thickness evolution of the six upper soil layers, including peat, above the granitic bedrock is also taken into account. Preliminary simulations are able to represent permafrost development at a high spatial resolution with evidence of important feedbacks due to permeable soil layers and faults in the bedrock that focus groundwater flow and solute transport.

How to cite: Cohen, D., Zwinger, T., Koskinen, L., and Karvonen, T.: Long-term coupled permafrost-groundwater interactions at Olkiluoto, Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8972, https://doi.org/10.5194/egusphere-egu2020-8972, 2020.

EGU2020-9741 | Displays | CR3.1

Mapping glacier lakes in Peru

Joanne Wood, Stephan Harrison, Ryan Wilson, Christian Yarleque, Georgie Bennett, Adriana Caballero, Janina Castromonte, Adam Emmer, David Garay, Henrry Garrido, Neil Glasser, W. Harrinson Jara, John Reynolds, Sarah Shannon, Richard Chase Smith, Edelwis Gina Soto, Tito Tinoco, Juan Carlos Torres, Efrain Turop, and Oscar Vilca and the Project GLOP

One consequence of current and likely future melting of high mountain glaciers is the development of glacial lakes. Their evolution over time has implications for future water supplies in arid mountains and for the timing and magnitude of glacier hazards, such as Glacial Lake Outburst Floods (GLOFs).

GLOF initiation depends on how lakes are connected to the glacial system, resulting from myriad processes such as the destabilisation of moraine dams and glacier front calving. To better understand these processes, we have undertaken an inventory of all glacier lakes in the Cordillera Blanca of Peru for 2019. We used manual digitisation from Landsat RGB at 30m resolution and have recorded the type of lake dam and its connection with surrounding glaciers and mountain slopes. We have also obtained lake inventories from INIAGEM (Instituto Nacional de Investigación en Glaciares y Ecosistemas de Montaña; 2016) and ANA (Autoridad Nacional del Agua; 2018), and have created an automatic inventory using the Normalised Difference Water Index and Normalised Difference Snow Index in Google Earth Engine. In this presentation we compare these different inventories and discuss both the methods and effectiveness of each for understanding GLOF hazards in the Peruvian Andes. 

How to cite: Wood, J., Harrison, S., Wilson, R., Yarleque, C., Bennett, G., Caballero, A., Castromonte, J., Emmer, A., Garay, D., Garrido, H., Glasser, N., Jara, W. H., Reynolds, J., Shannon, S., Smith, R. C., Soto, E. G., Tinoco, T., Torres, J. C., Turop, E., and Vilca, O. and the Project GLOP: Mapping glacier lakes in Peru, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9741, https://doi.org/10.5194/egusphere-egu2020-9741, 2020.

EGU2020-17330 | Displays | CR3.1

Towards a global assessment of future glacial lakes and related hazards, risks and opportunities

Holger Frey, Christian Huggel, Simon Allen, Adam Emmer, Dan Shugar, Daniel Farinotti, Matthias Huss, and Horst Machguth

The formation of new lakes in areas uncovered by retreating glaciers is a phenomenon that is often accompanying glacier retreat. On the one hand, such glacial lakes constitute a potential source of hazards and risks in the form of glacial lake outburst floods (GLOFs), but also amplify the potential reach of other mass movements when involved in cascading process chains. On the other hand, these new lakes might provide opportunities as well, as they are attractive elements in changing mountain landscapes and provide a significant water storage and hydropower potential. Here, we present an approach to establish the first global assessment of the characteristics, risks and opportunities provided by the formation of new lakes in glacierized mountain regions. This study is currently in the phase of concept development, in our contribution we present the planned methodological steps and some preliminary results.

In our approach, we draw on recently published datasets of ice thickness distributions of all glaciers around the world to detect the sites of potential future lake formation and extract general characteristics, such as lake depth and volume, as well as the elevation distribution. In combination with a new global glacial lake inventory, we estimate the total number of glacial lakes for each of the world’s mountain ranges, and contrast the share of already existing glacial lakes with the share of potential future glacial lakes. In combination with a global glacier evolution model (GloGEM), formation dates of these future lakes are estimated, considering different RCPs.

A major focus will be put on the assessment of regional hazards and risks. By analyzing the topographic potential around all future lakes from digital elevation information and a globally complete glacier inventory (RGI), the susceptibility for mass movement impacts is assessed in a generic way for each lake. Simple flow routing modeling will be used to evaluate the potential downstream impact. In combination with census data and other socio-economic indicators, a preliminary danger or risk assessment can be made in order to identify future hotspots of GLOF risks. In combination with globally available data on glacier runoff contributions to streamflow, regions are identified where more detailed evaluations of the water storage potential provided by such new lakes are of particular relevance.

The results of this work will allow anticipating hotspots of potential future GLOF hazards and risks at a local to global level. Further, important information to decision makers will be provided for long term planning regarding risk and water resources management as well as climate change adaptation measures and taking advantage of the opportunities provided by the formation of new glacial lakes.

How to cite: Frey, H., Huggel, C., Allen, S., Emmer, A., Shugar, D., Farinotti, D., Huss, M., and Machguth, H.: Towards a global assessment of future glacial lakes and related hazards, risks and opportunities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17330, https://doi.org/10.5194/egusphere-egu2020-17330, 2020.

EGU2020-17689 | Displays | CR3.1

Identifying key predictors for the susceptibility of Himalayan glacial lakes to sudden outburst floods

Melanie Fischer, Georg Veh, Oliver Korup, and Ariane Walz

Despite being a rather rare phenomenon when compared to the occurrence rates of other alpine hazards (e.g. landslides, avalanches), glacial lake outburst floods (GLOFs) pose a significant threat to downvalley communities in glaciated mountain areas. Characteristically high peak discharge rates and flood volumes, documented to have reached 30,000 m³/s and > 50 million m³ in the past century, not only provide GLOFs with a landscape-forming potential but also killed a reported global total of > 12,000 people and caused severe damage to infrastructures. Extensive glacial covers and steep topographic gradients, coupled with rapidly changing socio-economical implications, make the Hindu-Kush-Himalaya (HKH) a high priority region for GLOF research, even though recent studies suggest an annual occurrence rate of 1.3 GLOFs per year across this range during the past three decades. So far, GLOF research in the greater HKH region has been predominantly focused on the classification of potentially dangerous glacial lakes derived from analysing a limited number of glacial lakes and even fewer reportedly GLOF-generating glacial lakes. Moreover, subjectively set thresholds are commonly used to produce GLOF hazard classification matrices. Contrastingly, our study is aimed at an unbiased, statistical robust and reproducible assessment of GLOF susceptibility. It is based on the currently most complete inventory of GLOFs in the HKH since the 1980’s, which comprises 38 events. In order to identify key predictors for GLOF susceptibility, a total of 104 potential predictors are tested in logistic regression models. These parameters cover four predictor categories, which describe each glacial lake’s a) topography, b) catchment glaciers, c) geology and seismicity in its surroundings, and c) local climatic variables. Both classical binary logistic regression as well as hierarchical logistic regression approaches are implemented in order to assess which factors drive susceptibility of HKH glacial lakes to sudden outbursts and whether these are regionally distinct.

How to cite: Fischer, M., Veh, G., Korup, O., and Walz, A.: Identifying key predictors for the susceptibility of Himalayan glacial lakes to sudden outburst floods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17689, https://doi.org/10.5194/egusphere-egu2020-17689, 2020.

Rock mechanics and its numerical representation alone are challenging tasks – if you add ice to that equation, it becomes an even more complex thing to do. Nevertheless, aiming for a better understanding of rock slopes in permafrost conditions and their mechanical behaviour depending on the scale and mechanisms of interest, integrating rock and joint characteristics, also including ice can become relevant. Krautblatter et al. (2013) suggests a rock-ice mechanical model, that describes the dominating effects for the stability of high-alpine rock slopes in permafrost conditions. This study aims to select ice filled rock joints as one of the relevant effects of Krautblatter et al. (2013) and combines it with findings of the laboratory test and derived temperature dependent failure criteria of Mamot et al. (2018). We present data and strategies for implementing temperature-dependent failure criteria for ice-filled rock interfaces into numerical distinct element code and their calibration by a comparison with preceding laboratory tests. Additionally, methods for temperature transfer within the model are suggested as well as for integrating stress-dependent application of different failure criteria in the numerical formulation. Here we show a benchmark joint-constitutive-model for rock-ice mechanical systems and its implementation in a comprehensive distinct element code.

How to cite: Pläsken, R., Julian, G., Michael, K., and Philipp, M.: Stress- and temperature dependent application of joint-constitutive-models for rock-ice mechanical systems and its implementation in a comprehensive distinct element code, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18754, https://doi.org/10.5194/egusphere-egu2020-18754, 2020.

EGU2020-20375 | Displays | CR3.1

Climate change and cryosphere in high mountains: preliminary results of field monitoring at Capanna Margherita hut, Punta Gnifetti (Monte Rosa, Pennine Alps)

Marco Giardino, Antonio Montani, Andrea Tamburini, Francesco Calvetti, Alessandro Borghi, Walter Alberto, Fabio Villa, Davide Martelli, Graziano Salvalai, and Luigi Perotti

In the last decades, climate change effects are spreading on cryosphere of mid latitude high mountains, affecting all environmental and territorial components. The Italian Alpine Club (CAI) is a privileged institution for observing climate change effects on cryosphere in high mountains, as well as for supporting scientists to proper assessment studies of related natural hazards, exposure, vulnerability effects, particularly those around alpine refuges and access routes. CAI has started a cooperative research with University of Torino (UniTO), Politecnico of Milano (PoliMI) and IMAGEO srl, focused in deglaciation, permafrost degradation and slope instabilities at the Punta Gnifetti peak (“Signal Kuppe, 4554 m a.s.l.), Monte Rosa (Pennine Alps, border between Italy and Switzerland). Here is the Margherita Hut, the highest refuge in Europe and a physical-meteorological observatory, as well as home to medical and scientific UniTO laboratories.

Activities started on May 2019 with a retrospective collection and interpretation of photos and archival news on the Punta Gnifetti environment. Multi-temporal geomorphological settings are compared to meteorological historical series for creating a morphoclimatic "timeline".

Instrumental monitoring and in situ field work began on August 2019, including: 1) determination of the ice thickness of the glacial cover by using georadar; 2) characterization of the geomechanical structure of the rock mass by means of terrestrial laser scanner; 3) establishment of a topographical reference point and georeferencing of all measuring points; 4) collection of litho-structural and geomorphological data for a reference geological model of the Punta Gnifetti; 5) photogrammetric helicopter flight for the 3D reconstruction of the site; 6) direct measurements of internal areas in order to obtain as-built building plans; 7) assessment of building services.

Preliminary results are presented here, together with directions for an effective data collection to be continued on 2020, including comparative analyses designated to: a) identify the relevant geomechanical features for rock mass stability; b) verify presence of ice inside fractures; c) reconstruct the ice-covered morphology of the Punta Gnifetti peak.

How to cite: Giardino, M., Montani, A., Tamburini, A., Calvetti, F., Borghi, A., Alberto, W., Villa, F., Martelli, D., Salvalai, G., and Perotti, L.: Climate change and cryosphere in high mountains: preliminary results of field monitoring at Capanna Margherita hut, Punta Gnifetti (Monte Rosa, Pennine Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20375, https://doi.org/10.5194/egusphere-egu2020-20375, 2020.

EGU2020-21229 | Displays | CR3.1

Modelling glaciers bed overdeepenings and possible future lakes in deglaciating landscapes of the French Alps

Maeva Cathala, Florence Magnin, Andreas Linsbauer, Wilfried Haeberli, Ludovic Ravanel, and Philip Deline

Alpine glacier retreat due to global warming generates major landscape changes in high mountain environments. New lakes can potentially form in Glaciers Bed Overdeepenings (GBOs). Those new water bodies, sometimes located near potentially instable slopes or behind unstable moraine dams, can increase outburst flood hazards, generating risks for valley floors. Such GLOF events (Glacial Lake Outbrust Floods) can result from displacement waves triggered by rock fall into lakes and/or sudden dam breaching. Those events can travel far down to low altitude areas and turning into high magnitude debris flows. Beyond the threats, those lakes can also represent opportunities for tourism, hydropower production or fresh water supply.

 

Anticipating location and formation of potential future lakes is thus essential for risk mitigation and seizing the opportunities. In the French Alps so far, potential future lakes have only been investigated in the Mont Blanc massif, while several other glaciated high mountain ranges may also yield water bodies in the near future. This study aims to identify and characterize the location of potential future lakes for each mountain massif of the French Alps (mainly the Mont Blanc, Grandes Rousses, Vanoise and Écrins massifs).

 

To do so, we first ran GlabTop model, a GIS scheme calculating ice thickness from surface slope via basal shear stress, to map potential GBOs. We also ran GlabTOP 2, which is based on the same concept but is fully automated. In this study, we compared the results between GlabTop and GlabTop 2. We then estimated the level of confidence of the predicted GBOs using morphometric analysis (slope angle at GBOs and downstream, presence/absence of crevasse fields, presence/absence of bedrock threshold) and classification of lakes according to their susceptibility of formation.

 

GlabTOP output thus revealed 89 GBOs (>1ha) which can potentially be sites for future lakes. 20 lakes are predicted in Écrins, 2 in Grandes Rousses, 39 in Vanoise and 30 on the French side of the Mont Blanc massif. The lakes with the highest surfaces/thicknesses are situated in the latter. Among the 89 predicted water bodies, 41 are highly susceptible to be formed. Some can already be observed in GBOs in recently deglaciated areas like at the Bionnassay and Tré la Tête glaciers (Mont Blanc massif).

 

This communication will present the approach, the detailed results and possible implications for landscape management at the French Alps scale.

How to cite: Cathala, M., Magnin, F., Linsbauer, A., Haeberli, W., Ravanel, L., and Deline, P.: Modelling glaciers bed overdeepenings and possible future lakes in deglaciating landscapes of the French Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21229, https://doi.org/10.5194/egusphere-egu2020-21229, 2020.

CR3.2 – Modelling and measuring snow processes across scales

EGU2020-19408 | Displays | CR3.2

Snowpack modelling in central Italy: analysis and comparison of high-resolution WRF-driven Noah LSM and Alpine3D simulations

Edoardo Raparelli, Paolo Tuccella, Rossella Ferretti, and Frank S. Marzano

Italy is a territory characterized by complex orography. Its main mountain chains are the Alps, which identify the northern Italian border, and the Apennines, which cross the entire Italian peninsula ranging from north-west to south-east. The major Apennines peaks reach almost 3000 meters and are located in central Italy, in the Abruzzo region. The near Mediterranean sea is an important source of moisture, which permits to this region to experience a substantial snow cover during winter. Thanks to the orientation of the Apennines chain and the height of its peaks the Abruzzo region is characterized by different climate types. This affects the precipitation patterns and the snowpack evolution, resulting in high regional variability of the snow cover. The goal of this study is to investigate the snow cover evolution in the Abruzzo region, using and comparing different snowpack models. To this end we have used the Weather Research and Forecasting (WRF) model to drive the Noah Land Surface Model (LSM) and the sophisticated three-dimensional snow cover model Alpine3D to simulate the snow cover evolution at regional scale. Noah LSM is already on-line coupled with WRF, but this is not the case for Alpine3D. Thus we have modified and used the interfacing library MeteoIO to force Alpine3D with the meteorological data simulated with WRF, off-line coupling the two models. We have validated the WRF simulation using a dense network of automatic weather stations (AWS), obtaining good agreement between simulated and observed data. We have found that the snow depth simulated with Noah LSM presents a negative bias, caused by the inability of the model to reproduce correctly the snow densification rate. Instead, Alpine3D is capable to better reproduce the observed densification rate, thanks to its more detailed description of the snow metamorphism processes. However, the snow depth simulated with Alpine3D presents a negative bias, caused by an underestimation of the new snow depth, which has a negative impact on the entire simulation.

How to cite: Raparelli, E., Tuccella, P., Ferretti, R., and Marzano, F. S.: Snowpack modelling in central Italy: analysis and comparison of high-resolution WRF-driven Noah LSM and Alpine3D simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19408, https://doi.org/10.5194/egusphere-egu2020-19408, 2020.

EGU2020-20859 | Displays | CR3.2

The importance of modelled processes in the evolution of snow cover versus snow mass

Lawrence Mudryk, Gerhard Krinner, Chris Derksen, Maria Santolaria-Otin, Martin Menegoz, Claire Brutel-Vuilmet, Carrie Vuyovich, Sujay Kumar, and Rhae Sung Kim

Conventional wisdom holds that confidence in future projections of snow cover extent and snow mass requires an understanding of the expected changes in future snow characteristics as a function of modelled snow processes. We will highlight contrasting results which suggest differing importance in the role of sub-grid scale processes on simulations of seasonal snow.

The first study is an evaluation of simulated snow cover extent projections from models participating in the 6th phase of the World Climate Research Programme Coupled Model Inter-comparison Project (CMIP-6). We demonstrate a single linear relationship between projected spring snow extent and global surface air temperature (GSAT) changes, which is valid across all future climate scenarios. This finding suggests that Northern Hemisphere spring snow extent will decrease by about 8% relative to the 1995-2014 level per °C of GSAT increase. The sensitivity of snow to temperature forcing largely explains the absence of any climate change pathway dependency, similar to other fast response components of the cryosphere such as sea ice and near surface permafrost.

The second study makes use of an ensemble of land surface models, downscaled to 5 km resolution across North America over the 2009-2017 period. In this case, uncertainty in total North American snow mass is dominated by differences among land surface model configurations. While the largest absolute spread in snow mass is found in mountainous regions, heavily vegetated boreal regions have the largest fractional spread compared to climatological values. In particular, differences in rain-snow partitioning and sublimation rates control the largest portions of the total uncertainty. These results suggest that projections of future snow mass depend specifically on how such processes are modelled and parameterized.

How to cite: Mudryk, L., Krinner, G., Derksen, C., Santolaria-Otin, M., Menegoz, M., Brutel-Vuilmet, C., Vuyovich, C., Kumar, S., and Kim, R. S.: The importance of modelled processes in the evolution of snow cover versus snow mass, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20859, https://doi.org/10.5194/egusphere-egu2020-20859, 2020.

EGU2020-5467 | Displays | CR3.2

Testing a Naive Snow Theory Against a Physically Based Model: Sensitivity of Global Mountain Snow Regimes to Increased Air Temperatures

Ross Woods, Juan Ignacio López Moreno, Esteban Alonso-Gonzalez, Jesus Revuelto, Joshua Larsen, and Bettina Schaefli

Mountain snow regimes will be significantly altered by climate warming, resulting in shallower snowpacks whose duration is also reduced. The sensitivity of snowpacks to a unit of air temperature warming depends strongly on climate; in addition, for a given climate, the sensitivity also depends on the details of energy balance partitioning. A synthesis of these factors remains challenging. Here we evaluate to what extent a naïve theory of snowpack response to warming can reproduce the sensitivity which is calculated by a detailed physically based model of the snowpack (Snobal), applied to a diverse global set of mountain locations. Our hypothesis is that the naïve theory will adequately predict the range of snow sensitivity values across diverse climates, but not the additional impacts of inter-site differences in energy partitioning for a given climate. The potential benefits of the naïve theory are that it enables a significant reduction of the uncertainty of snowpack sensitivity, and an improved conceptual understanding of the impacts of climate parameters (e.g. the seasonality and fluctuations of temperature and precipitation) on snowpack accumulation and melt-sensitivity under warming climates.

How to cite: Woods, R., López Moreno, J. I., Alonso-Gonzalez, E., Revuelto, J., Larsen, J., and Schaefli, B.: Testing a Naive Snow Theory Against a Physically Based Model: Sensitivity of Global Mountain Snow Regimes to Increased Air Temperatures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5467, https://doi.org/10.5194/egusphere-egu2020-5467, 2020.

EGU2020-10217 | Displays | CR3.2

Latest scientific and technical evolutions in the Crocus snowpack model

Matthieu Lafaysse, Marie Dumont, Rafife Nheili, Léo Viallon-Galinier, Carlo Carmagnola, Bertrand Cluzet, Mathieu Fructus, Pascal Hagenmuller, Samuel Morin, Pierre Spandre, François Tuzet, and Vincent Vionnet

This contribution presents an overview of the last stable release of the Crocus detailed snowpack model in the SURFEX opensource modelling platform. It gathers numerous recent scientific and technical developments in a common code version. An explicit representation of the evolution of light absorbing particles mass in snow (e.g. black carbon, mineral dust) allows representing their impact on solar radiation absorption in the snowpack in the visible and near-infrared spectrum through the TARTES optical scheme, and the consequences on all snowpack properties. Crocus is now coupled to the MEB (Multiple Energy Balance) vegetation scheme and can therefore be applied on forested areas. A module of snow management including grooming and snow making can also be optionally activated to simulate the snowpack on ski slopes. Developments used in the French operational system in support of avalanche hazard forecasting were also fully integrated in SURFEX: the SYTRON module for snow erosion and accumulation by the wind and the expert system MEPRA which analyses the mechanical stability of the simulated snowpacks. Finally, an ensemble multiphysics version of the model (ESCROC) was also developed by implementing from 2 to 4 parameterizations from the literature for each physical process represented by an uncertain empirical parameterization. The different combinations enable the quantification of simulations uncertainty required in various applications: future projections of snow cover; sensitivity analyses of a given process ; data assimilation of snow observations. Crocus and ESCROC are included in the ESM-SnowMIP model intercomparison and exhibit a robust skill in various climates and environments. Several running-time optimizations were also implemented in the latest release. We present an overview of the current numerical cost with a comparison to more classical snow schemes used in NWP and climate model applications. The code is provided through a git repository and with a simple visualization software to help users to display snowpack internal properties at local scale. On-going works are focused on the implementation of new data assimilation algorithms well suited to the numerical specificities of this scheme. An externalized version for coupling with other surface schemes is currently under development.

How to cite: Lafaysse, M., Dumont, M., Nheili, R., Viallon-Galinier, L., Carmagnola, C., Cluzet, B., Fructus, M., Hagenmuller, P., Morin, S., Spandre, P., Tuzet, F., and Vionnet, V.: Latest scientific and technical evolutions in the Crocus snowpack model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10217, https://doi.org/10.5194/egusphere-egu2020-10217, 2020.

EGU2020-17783 | Displays | CR3.2

Process-based simulation of snow cover evolution in ski resorts using the AMUNDSEN model: results and validation

Florian Hanzer, Daniel Günther, Ulrich Strasser, Valentina Premier, Mattia Callegari, Carlo Marin, and Claudia Notarnicola

Snow management, i.e., snowmaking and grooming, is an integral part of modern ski resort operation. While the current snow cover distribution on the slopes is often well known thanks to the usage of advanced monitoring techniques, estimates about its future evolution are usually lacking. Management-enabled numerical snowpack models driven by meteorological forecasts can help to fill this gap. In the frame of the H2020 project PROSNOW such software tools are developed to be run on an operational basis with the aim to optimize snow management as well as the use of water and energy resources. As part of PROSNOW, model simulations for the ski resorts Seefeld and Obergurgl (both Austria) as well as Colfosco and San Vigilio (both Italy) are performed with the physically based snow model AMUNDSEN. In its particular snow management module, both socioeconomic and physical factors are considered, the former concerning the decision when, where and how much snow should be produced, and the latter considering the snowmaking conditions, i.e., how much snow can be produced in the current ambient conditions (in terms of temperature and humidity) and the given ski resort infrastructure (number and efficiency of snow guns, water availability, etc.).

In our contribution we show the implementation of snowmaking and grooming practices in the AMUNDSEN model, its adaptation to individual ski resorts, and how different potential snow management strategies are accounted for. Model results obtained using historical meteorological observations and hindcast simulations are validated against observations from numerous data sources such as Sentinel-2 snow cover maps, distributed snow depth measurements from groomers, temperature and humidity measurements from snow guns as well as water consumption recordings.

How to cite: Hanzer, F., Günther, D., Strasser, U., Premier, V., Callegari, M., Marin, C., and Notarnicola, C.: Process-based simulation of snow cover evolution in ski resorts using the AMUNDSEN model: results and validation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17783, https://doi.org/10.5194/egusphere-egu2020-17783, 2020.

The snowpack continuously evolves due to metamorphic and mechanical processes. Understanding and quantifying these processes and in particular their complex interplay and impact on the snowpack's strength is challenging, yet of large interest to the snowpack modeling community. Due to the layer representation and the absence of an explicit numerical solution of the mass continuity equation in common snowpack models, competing effects of mechanical settling and phase changes (e.g. due to vapor transport) can hardly be assessed faithfully. Towards a remedy, we investigate the potential of a numerical scheme that treats the vapor recrystallization term on a moving mesh as imposed by the settling term of the continuity equation.
First, we introduce a continuum mechanical snowpack model that explicitly accounts for both water vapor transport induced by temperature gradients, and settling processes. Next, we describe a computational approach to solve the coupled snowpack model. Water vapor transport as a result of temperature and condensation rate evolution are solved by means of a finite difference scheme. Accounting for settling processes requires to solve an additional ice volume balance, which is done based on the method of characteristics. Its advantage is that it can exactly account for the moving upper free surface of the snowpack. Unstructured meshes enable us to track (potentially densifying) snow layers at high spatial resolution. A closure for the settling velocity is formulated in terms of stresses from the overburdened snow mass and snow viscosity. The proposed continuum-mechanical snowpack model enables us for the first time to investigate the coupled interplay and relative importance of water vapor transport and snowpack settling on time scales from minutes to several hours. 
In a series of numerical examples, we present simulation results for varying snow heights (0.02 - 1 m), snow densities (100 - 917 kgm-3) and temperature gradients (20, 100, 1000 Km-1) to assess the effect of simultaneous snowpack settling and water vapor transport. The proposed model allows us to observe the downward propagation of a snow layer interface coupled to water vapor deposition and sublimation, at high spatial resolution. One of our major findings is that while settling might strongly increase ice densities, it also has an additional (weaker) impact on the condensation rate. Finally, we will discuss to which extent the proposed novel computational approach could be used to study and quantify the interplay of coupled mechanical and metamorphic processes in future community snowpack models, for instance while identifying regimes that require to account for process coupling.

How to cite: Simson, A., Kowalski, J., and Löwe, H.: Numerical solution of the mass continuity equation for snowpack modeling on moving meshes: Coupling between mechanical settling and water vapor transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10629, https://doi.org/10.5194/egusphere-egu2020-10629, 2020.

EGU2020-21893 | Displays | CR3.2

The RHOSSA campaign: Multi-resolution monitoring of the seasonal evolution of the structure and mechanical stability of an alpine snowpack

Neige Calonne, Betti Richter, Henning Löwe, Cecilia Cetti, judith Ter Schure, Alec Van Herwiijnen, Charles Fierz, Matthias Jaggi, and Martin Schneebeli

The necessity of characterizing snow through objective, physically-motivated parameters has led to new model formulations and new measurement techniques. Consequently, essential structural parameters such as density and specific surface area (for basic characterization) or mechanical parameters such as the critical crack length (for avalanche stability characterization) gradually replace the semi-empirical indices acquired from traditional stratigraphy. These advances come along with new demands and potentials for validation. To this end, we conducted the RHOSSA field campaign, in resemblance of density (ρ) and specific surface area (SSA), at the Weissfluhjoch research site in the Swiss Alps to provide a multi-instrument, multi-resolution dataset of density, SSA, and critical crack length over the complete winter season 2015-2016. In this paper, we present the design of the campaign and a basic analysis of the measurements alongside with predictions from the model SNOWPACK. To bridge between traditional and new methods, the campaign comprises traditional profiles, density cutter, IceCube, SnowMicroPen (SMP), micro-computed-tomography, propagation saw tests, and compression tests. To bridge between different temporal resolutions, the traditional weekly to bi-weekly snow pits were complemented by daily SMP measurements. From the latter, we derived a re-calibration of the statistical retrieval of density and SSA for SMP version 4 that yields an unprecedented, spatio-temporal picture of the seasonal evolution of density and SSA in a snowpack. Finally, we provide an inter-comparison of measured and modeled estimates of density and SSA for 4 characteristic layers over the entire season to demonstrate the potential of high temporal resolution monitoring for snowpack model validation.

How to cite: Calonne, N., Richter, B., Löwe, H., Cetti, C., Ter Schure, J., Van Herwiijnen, A., Fierz, C., Jaggi, M., and Schneebeli, M.: The RHOSSA campaign: Multi-resolution monitoring of the seasonal evolution of the structure and mechanical stability of an alpine snowpack, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21893, https://doi.org/10.5194/egusphere-egu2020-21893, 2020.

EGU2020-11824 | Displays | CR3.2

An implicit physical water percolation model

Willem Jan van de Berg

The parametrization in numerical models of the behavior of water in snow is either oversimplified - the bucket method – or hugely complicated – the Richardson equation. The latter faithfully resembles the general behavior of water in snow, when a dual domain approach, representing slow matrix and fast preferential flow, is taken. However, this type of models are unsuitable for application in climate models due to their high computation costs.

Therefore, an implicit Richardson equation model is developed, which is able to run on time steps of several minutes, typical for climate models, and snow layer thickness down to a few centimeters. In order to reach to a differentiable governing equation, required for iterative implicit time stepping, with as few as possible discontinuities in the derivatives, favorable for convergence, modifications are made in the governing equations when the water content approaches the irreducible water content or water almost fills the available pore space. Here, we show the first results of this model, with a focus on the impact of parameterization choices on the modelled water flow, refreezing profile and melt water buffering capacity.

How to cite: van de Berg, W. J.: An implicit physical water percolation model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11824, https://doi.org/10.5194/egusphere-egu2020-11824, 2020.

EGU2020-18125 | Displays | CR3.2

Simple estimations of new and bulk snow density in the Italian Alps: Lessons from a decade of distributed observations

Nicolas Guyennon, Franco Salerno, Mauro Valt, Anna Bruna Petrangeli, Rosa Maria Salvatori, and Emanuele Romano

The Snow Water Equivalent (SWE), combining the information of snow depth and snow density is a necessary variable for snow-hydrological studies and applications, as well as, for ecological function or avalanche forecasting. Direct automatics measurements of SWE requires an easy access to the monitoring site while manual measurements are costly and challenging. On the other hands, physically based models for snow density estimates require local meteorological data limiting their application in complex topography such as mountains areas. For this reason, different empirical regressions methods for the characterization of SWE and associated variability have been proposed for regional studies. In this study, we report our experience based on simple regression models able to characterize the new snow density and the snow bulk density at the scale of the entire Italian Alps, taking advantage of a decade of distributed observations. 12112 snowfall observations (2005-2015) gathered at 122 stations, ranging from 650 m to 2858 m a.s.l., have been analyzed to characterize the new snow density. 6078 snowpack depth and bulk density measurements (2009-2018) from 150 sites, ranging from 640 m to 3400 m a.s.l., have been collected to investigate the snow bulk density.

The mean air temperature of the 24 hours preceding the snowfall event, as a proxy of the transformation of freshly-fallen snow, has been found to be the best predictor of the new snow density, within 30% of uncertainty over the whole Italian Alps. While monthly regression allows considering part of the snow state variability through seasonality, the analysis of the associated residues suggests that, in the lack of local wind field information, the adoption of a local approach is not able to substantially increase the predictive capabilities of the model. The snow bulk density variability mainly responds to seasonality and can be estimated adopting the day of the year, as a proxy of the combined effect of compaction through seasonal snow accumulation and partial melting during the late season. Such approach enables a continuous (along the season) description of the SWE variation within 15% of uncertainty, similar to the within-site variability, presenting even better performances during the late season through the introduction of non-linearity. Differently from new snow density, regionalization performed considering separately those regions close to the sea improves the overall performances.

Although more performing models have already been proposed, the variables necessary to feed the proposed regressions (i.e. mean air temperature for new snow density and the day of the year for the bulk snow density) are easy to be acquired, making the proposed models valuable tools either in case of low instrumented watersheds or for past reconstruction. Finally, the low number of parameters to be calibrated makes the proposed regressions easy to be tested in other regions.  

How to cite: Guyennon, N., Salerno, F., Valt, M., Petrangeli, A. B., Salvatori, R. M., and Romano, E.: Simple estimations of new and bulk snow density in the Italian Alps: Lessons from a decade of distributed observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18125, https://doi.org/10.5194/egusphere-egu2020-18125, 2020.

EGU2020-1468 | Displays | CR3.2

Why is Snow Slippery? The Role of Abrasion in Snow Kinetic Friction

James Lever, Susan Taylor, Garrett Hoch, and Emily Asenath-Smith

The mechanics of snow friction are central to competitive skiing, safe winter driving, avalanche dynamics, and efficient Polar sleds. For nearly 80 years, prevailing theory has postulated self-lubrication: dry-contact sliding warms snow-grains to the melting point, and further sliding produces melt-water that lubricates the interface. We recently published micro-scale interface observations that contradicted this explanation: contacting snow grains abraded and did not melt under a polyethylene slider, despite low friction values. We obtained coordinated infrared, visible-light, and scanning-electron micrographs that confirm that the evolving shapes observed during our tribometer tests are contacting snow grains polished by abrasion, and that the wear particles can sinter together and fill the adjacent pore spaces. Furthermore, dry-contact abrasive wear reasonably predicts the evolution of snow-slider contact area, and sliding-heat-source theory confirms that contact temperatures would not reach 0°C during our tribometer tests. Importantly, published measurements of interface temperatures also indicate that melting did not occur during field tests on sleds and skis. We postulate that abraded ice crystals form a dry-lubricant layer that makes contacting snow-grains slippery and are currently undertaking additional observations and theoretical analyses to assess this hypothesis.

How to cite: Lever, J., Taylor, S., Hoch, G., and Asenath-Smith, E.: Why is Snow Slippery? The Role of Abrasion in Snow Kinetic Friction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1468, https://doi.org/10.5194/egusphere-egu2020-1468, 2020.

EGU2020-11313 | Displays | CR3.2

Scaling behavior of lidar-derived snow depth across the semi-arid Chilean Andes

Pablo Mendoza, Thomas Shaw, Fabiola Pinto, Miguel Lagos, Jesús Revuelto, Keith Musselman, Shelley MacDonell, and James McPhee

The seasonal melt of mountain snow-cover provides a vital source of freshwater for downstream systems, sustaining multiple productive uses, population needs, and unique ecosystems. In the semi-arid Andes Cordillera, the snowpack acts as a natural water reservoir, releasing spring snowmelt runoff that accounts for more than 60 % of the total annual streamflow. Hence, understanding and characterizing the spatial variability of snow over this large domain is critical for accurate hydrological predictions. We examine the probability density functions and the geostatistical structure of snow depth through variogram analysis, using terrestrial lidar scans acquired during two seasons (2018 and 2019). First, we compare the spatial patterns of snow depth near maximum accumulation at three experimental sites: (i) the Tascadero catchment (-31.26°N, 3270-3790 m a.s.l.), (ii) the Las Bayas experimental catchment (-33.31°N, 3218-4022 m a.s.l.); and (iii) the Valle Hermoso catchment (-36.91°N, 1449-2563 m a.s.l.). Second, we analyze the inter- and intra-annual variability of snow depth patterns in the Las Bayas catchment, where seven scans were acquired during seasons 2018 and 2019. 

The comparison across sites reveals snow depth fractal behavior until a first omnidirectional scale break in the range 15-22 m for unvegetated areas, and a short-range fractal dimension spanning 2.5-2.65. In the woodland of Valle Hermoso, a much shorter (5 m) scale break and a larger short-range fractal dimension (2.73) are found. Secondary scale ranges and breaks spanning 62-125 m are found in all sites but Tascadero, where snow depth follows a bimodal distribution across the domain. In the Las Bayas domain, inter-annual consistency is found in snow scaling patterns, with two distinct regions separated by a short scale break ~6 m early in the winter, increasing to larger break lengths (15-18 m) in July and August. These results help to inform about the appropriate spatial configuration for snowpack modeling across the Andes. Efforts to better understand the modulation of topography (slope and wind exposure) and vegetation on snow depth distribution patterns, as well as impacts of dominant wind directions on anisotropies in fractal parameters, are ongoing.

How to cite: Mendoza, P., Shaw, T., Pinto, F., Lagos, M., Revuelto, J., Musselman, K., MacDonell, S., and McPhee, J.: Scaling behavior of lidar-derived snow depth across the semi-arid Chilean Andes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11313, https://doi.org/10.5194/egusphere-egu2020-11313, 2020.

EGU2020-14575 | Displays | CR3.2

Towards a scale-independent fractional snow-covered area parameterization for complex terrain

Nora Helbig, Yves Bühler, Lucie Eberhard, César Deschamps-Berger, Simon Gascoin, Marie Dumont, Jeffrey Deems, and Tobias Jonas

Whenever there is snow on the ground, there will be large spatial variability in snow depth. The spatial distribution of snow is significantly influenced by topography due to wind, precipitation, shortwave and longwave radiation, and even snow avalanches relocate the accumulated snow. Fractional snow-covered area (fSCA) is an important model parameter characterizing the fraction of the ground surface that is covered by snow and is crucial for various model applications such as weather forecasts, climate simulations and hydrological modeling.

We recently suggested an empirical fSCA parameterization based on two spatial snow depth data sets acquired at peak of winter in Switzerland and Spain, which yielded best performance for spatial scales larger than 1000 m. However, this parameterization was not validated on independent snow depth data. To evaluate and improve our fSCA parameterization, in particular with regards to other spatial scales and snow climates (or geographic regions), we used spatial snow depth data sets form a wide range of mountain ranges in USA, Switzerland and France acquired by 5 different measuring methods. Pooling all snow depth data sets suggests that a scale-dependent parameter should be introduced to improve the fSCA parameterization, in particular for sub-kilometer spatial scales. Extending our empirical fSCA parameterization to a broader range of scales and snow climates is an important step towards accounting for spatio-temporal variability in snow depth in multiple snow model applications.

How to cite: Helbig, N., Bühler, Y., Eberhard, L., Deschamps-Berger, C., Gascoin, S., Dumont, M., Deems, J., and Jonas, T.: Towards a scale-independent fractional snow-covered area parameterization for complex terrain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14575, https://doi.org/10.5194/egusphere-egu2020-14575, 2020.

EGU2020-5918 | Displays | CR3.2

The growth of snow bedforms

Kelly Kochanski, Robert Anderson, and Gregory Tucker

Wind-blown snow does not lie flat. It self-organizes into dunes, waves, ripples, and anvil-shaped sastrugi. These features, called snow bedforms, are high-speed analogues of sand features barchans, ripples, and yardangs. Snow bedforms appear within hours or days after a blizzard, and may migrate as fast as several meters per hour. They are widespread, and affect the albedo and thermal properties of snow across the polar regions, but thus far they have attracted little attention within aeolian geomorphology.

For the past three winters, I have documented the growth of snow bedforms in Colorado Front Range. I present time-lapse footage showing the movement of snow dunes, ripples and sastrugi (see tinyurl.com/bedform-videos). These observations show that (1) snow is only flat when winds are slower than 6.4 m/s (2) snow dunes adjust minute-by-minute to changes in wind speed, (3) the most widespread bedform, sastrugi, evolve by migrating and eroding downwind, and (4) snow waves and dunes deposit layers of cohesive snow in their wakes, and thus aid snow deposition in windy conditions. These observations provide the basis for new conceptual models of bedform evolution based on the rates of snowfall, aeolian transport, erosion, and snow sintering across the snowscape.

How to cite: Kochanski, K., Anderson, R., and Tucker, G.: The growth of snow bedforms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5918, https://doi.org/10.5194/egusphere-egu2020-5918, 2020.

EGU2020-10368 | Displays | CR3.2

Detailed simulations of snow properties and accumulation across the Antarctic Ice Sheet

Jan Lenaerts, Eric Keenan, Nander Wever, Marissa Dattler, Carleen Reijmer, and Brooke Medley

Surface mass balance (SMB) represents a large uncertainty in characterizing Antarctic Ice Sheet (AIS) mass balance. Atmospheric reanalysis products, which are commonly used for AIS SMB studies, do not include small-scale snow redistribution processes even though these can be of the same order of magnitude as snow accumulation in many parts of the AIS. Therefore, a proper representation of these processes is critical to interpret local SMB and firn observations, such as from ICESat-2 repeat altimetry. In this study, we use a detailed, multi-layer snow model (SNOWPACK) forced by a global atmospheric reanalysis (MERRA-2). Firstly, we show that a new accumulation scheme, designed to better represent wind-driven snow compaction in SNOWPACK, substantially reduces simulated biases in near-surface snow density at 131 locations across the AIS. Next, we employ a distributed version of SNOWPACK to two regions on the AIS, and compare the simulation output to airborne radar and in-situ observations of SMB. Our results demonstrate that SNOWPACK can capture the timing of blowing snow events, snow erosion events, as well as observed kilometer-scale spatial SMB variability. This study illustrates the importance of using high-resolution SMB models when converting surface height (volume) observations to mass changes.

How to cite: Lenaerts, J., Keenan, E., Wever, N., Dattler, M., Reijmer, C., and Medley, B.: Detailed simulations of snow properties and accumulation across the Antarctic Ice Sheet , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10368, https://doi.org/10.5194/egusphere-egu2020-10368, 2020.

EGU2020-19249 | Displays | CR3.2

The genesis of a climate archive: snow pack studies at four polar sites

Johannes Freitag, Maria Hörhold, Alexander Weinhart, Sepp Kipfstuhl, and Thomas Laepple

Understanding the deposition history and signal formation in ice cores from polar ice sheets is fundamental for the interpretation of paleoclimate reconstruction based on climate proxies. Polar surface snow responds to environmental changes on a seasonal time scale by snow metamorphism, displayed in the snow microstructure and archived in the snowpack. However, the seasonality of snow metamorphism and its link to the deposited signal in isotopes and impurity load is poorly known.

Here, we apply core-scale microfocus X-ray computer tomography to continuously measure snow microstructure of four snow cores from Greenlandic (Renland ice cap-drill site (2m), EASTGRIP drill site (5m)) and Antarctic sites (EDML-drill site (3m), COFI7/Plateau station (4m)) covering a wide range of annual temperatures from -18°C down to -56°C. In our multi-parameter approach we compare the derived microstructural properties on the mm- to cm-scale to discretely measured trace components and stable water isotopes, commonly used as climate proxies. We will show how ice and pore intercepts, the geometrical anisotropy, specific surface area, crusts anomalies and small-scale density distributions are represented under different climate conditions. Their profiles will be discussed in the context of snow metamorphism and deposition history using trace components and isotopes as additional constraints on timing.

How to cite: Freitag, J., Hörhold, M., Weinhart, A., Kipfstuhl, S., and Laepple, T.: The genesis of a climate archive: snow pack studies at four polar sites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19249, https://doi.org/10.5194/egusphere-egu2020-19249, 2020.

CR3.3 – Snow avalanche dynamics: from basic physical knowledge to mitigation strategies

EGU2020-2153 | Displays | CR3.3

Numerical modeling of snow avalanche dynamics based on the Material Point Method

Xingyue Li, Betty Sovilla, Stephanie Wang, Chenfanfu Jiang, and Johan Gaume

Snow avalanches are one of the most dangerous and catastrophic hazards in mountainous regions, which cause fatalities and property losses. Understanding the dynamics of snow avalanches is essential for designing safe and optimised mitigation measures. This study presents numerical modeling of snow avalanche dynamics, based on the Material Point Method (MPM) and an elastoplastic constitutive model for porous cohesive materials. MPM is a hybrid Eulerian-Lagrangian numerical method, which can simulate processes with large deformation, collisions and fractures. The elastoplastic model consists of an ellipsoid yield surface, a hardening law, and an associative flow rule. It enables us to capture the mixed-mode failure of snow including tensile, shear and compressive failure. Both ideal and real terrains are modeled in our study. By varying the properties of snow on the ideal slope, the model can reproduce four typical reported flow regimes, namely, cold shear, warm shear, warm plug and slab sliding regimes. In addition, surges and roll-waves are observed especially for flows in the transition from cold shear to warm shear regimes. The evolution of the avalanche front, the free surface shape and the velocity vertical profile show distinct characteristics for the different flow regimes. In addition to the snow properties, slope angle and path length are changed to investigate their effects on the maximum velocity, the run-out distance and the avalanche deposit height. The relation between the maximum velocity and the run-out distance obtained from our MPM simulations is analyzed along with data collected from literature. Furthermore, we benchmark the MPM model by simulating snow avalanches on real terrain. The evolution of the avalanche front position and velocity from the MPM simulations are quantitatively compared with the measurement data from past studies.

How to cite: Li, X., Sovilla, B., Wang, S., Jiang, C., and Gaume, J.: Numerical modeling of snow avalanche dynamics based on the Material Point Method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2153, https://doi.org/10.5194/egusphere-egu2020-2153, 2020.

EGU2020-18607 | Displays | CR3.3 | Highlight

Simulating the propagation of wet snow avalanches: challenges and perspectives

Guillaume Chambon, Thierry Faug, Mohamed Naaim, and Nicolas Eckert

Recent winters saw a striking increase in wet snow avalanche activity. Compared to dry avalanches, wet snow avalanches present uniquely distinctive features such as slower velocities, larger depths, unusual trajectories and deposit shapes, and a paste-like rheology that can result in large shear and normal stresses. In addition, the behavior of wet avalanches may strongly vary depending on the actual snow liquid water content. Complex transitions between dry (cold) and wet (hot) behaviors have also been observed during the propagation of single avalanche events. Current numerical models of avalanche dynamics are challenged when it comes to capturing the full spectrum of these different regimes, and the transitions in between. In this contribution, we critically review the various rheological models that have been proposed in the literature to simulate dry and wet snow avalanches in the frame of depth-averaged shallow-flow approaches. On this basis, a simplified parametric rheological law is proposed, with the objective of representing both dry-like and wet-like behaviors and allowing for smooth transitions between them. The law is implemented in a robust 2D shallow-flow simulation code, and systematic sensitivity studies are performed on synthetic and real topographies. Simulation outcomes are analysed in terms of propagation dynamics and deposition patterns, and the ability of the model to capture both dry and wet regimes is discussed. Lastly, a specific calibration methodology is proposed to infer the relevant mechanical parameters from documented avalanche events.

How to cite: Chambon, G., Faug, T., Naaim, M., and Eckert, N.: Simulating the propagation of wet snow avalanches: challenges and perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18607, https://doi.org/10.5194/egusphere-egu2020-18607, 2020.

EGU2020-18565 | Displays | CR3.3 | Highlight

Avalanche flow regime transitions in a changing climate

Camille Ligneau, Betty Sovilla, and Johan Gaume

In the near future, climate change will impact the snow cover in Alpine regions. Higher precipitations and warmer temperatures are expected at lower altitude, leading to larger gradients of snow temperature, snow water content and snow depth between the top and the bottom of slopes. As a consequence, climate change will also indirectly influence the behavior of snow avalanches.

The present work aims to investigate how changes in snow cover properties will affect snow avalanches dynamics. Experimental studies allowed to characterize different avalanche flow regimes which result from particular combinations of snow physical and mechanical properties. In particular, expected variations of snow temperatures with elevation will cause more frequent and more extreme flow regime transitions inside the same avalanche. For example, a fast avalanche characterized by cold and low-cohesive snow in the upper part of the avalanche track will transform more frequently into a slow flow made of wet and heavy snow when the avalanche will entrain warm snow along the slope. A better understanding of these flow regime transitions, which have already been largely reported, is crucial, because it affects both daily danger assessment (e.g. forecasting services, road controls) and hazard mapping of avalanches.

To date, most avalanche modeling methods are not considering temperature effects and are then unable to simulate flow regime transitions and unprecedented scenarios. Our goal is then to develop a model capable of simulating reported flow regimes, flow transitions and the interactions between the snow cover and the flow (erosion, entrainment). Since these elements are not yet fully understood, we firstly model these mesoscopic processes using a 2D Discrete Element Model (DEM) in which varying particle cohesion and friction mimic the effect of changes in snow temperature. Flow regimes are simulated by granular assemblies put into motion by gravity on an inclined slope, which interact with a granular and erodible bed surface. Simulations are calibrated using experimental data coming from the avalanche test site located in Vallée de la Sionne, which record avalanches since more than 20 years. This modeling will then be used as an input to improve slope-scale models and make them more appropriate for avalanche risk management in the context of climate change.

How to cite: Ligneau, C., Sovilla, B., and Gaume, J.: Avalanche flow regime transitions in a changing climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18565, https://doi.org/10.5194/egusphere-egu2020-18565, 2020.

EGU2020-8133 | Displays | CR3.3

Spatial and temporal variability of snow avalanche impact pressure and its importance for structural design

Betty Sovilla, Michael Kyburz, Camille Ligneau, Jan-Thomas Fischer, and Mark Schaer

Measurements of snow avalanche impact pressures are performed at the Vallée de la Sionne test site since winter 1999. In these years of operation, we recorded the impact pressure of around 60 avalanches characterized by different flow regimes and dimensions.

Pressure measurements were performed, simultaneously, on three different structures which are spatially distributed with a maximum distance of 30 m, in the run-out zone of the Vallée de la Sionne test site. The structure widths range from 0.25 to 1 m. On these structures pressure sensors ranging from small cells with 0.10 to 0.25 m in diameter to large pressure plates with area of 1m2 are mounted at different heights.

A systematic analysis of all 60 avalanche data sets shows that the pressure measured at the different obstacles varies considerably, even within the same avalanche, both in space and time. Part of these differences can be attributed to different drag coefficients and dependence on obstacle size, but a large part of these differences can only be explained by the spatial variability of the flow properties and the temporal variability of the physical processes governing the interaction of the avalanche and the structures.

In this contribution we show how spatial and temporal impact pressure variabilities correlate to avalanche dimension and flow regimes and we discuss the implication of such variations for structural design and hazard mapping.

How to cite: Sovilla, B., Kyburz, M., Ligneau, C., Fischer, J.-T., and Schaer, M.: Spatial and temporal variability of snow avalanche impact pressure and its importance for structural design, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8133, https://doi.org/10.5194/egusphere-egu2020-8133, 2020.

Recent well-documented measurements on full-scale snow avalanches impacting civil engineering structures have identified an impact force regime for which the pressure exerted on the obstacle is depth-dependent, rather than being controlled by the square of the avalanche speed. In addition, these measurements have shown that the depth-dependent force could be many times greater than the hydrostatic force associated with the thickness of the incoming avalanche-flow. The present paper proposes a general analytic form for the impact force of dense avalanches on any kind of structure, with the help of the depth-averaged hydrodynamics applied to a control-volume surrounding the influence zone of the obstacle. This form extends the recently established force models for wall-like and pylon-like obstacles impacted by flows of dry granular materials. A criterion to distinguish between the depth-dependent force regime and the velocity-square force regime is derived. It is demonstrated that the size of the influence zone of the obstacle, relative to the dimension of the obstacle and/or the avalanche thickness, is a key ingredient---in addition to the traditional Froude number---to demarcate the depth-dependent from velocity-square impact forces. There is still a need for further developments to unravel the size and shape of the influence zone of any kind obstacle for any type of flowing snow, and then being able to hone this criterion as well as to predict the force amplification in the depth-dependent regime. However the present study takes a step forward for a better understanding of granular avalanche impact force on civil engineering structures.

How to cite: Faug, T.: Impact of dense avalanches on civil engineering structures: demarcating depth-dependent from velocity-squared impact forces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12725, https://doi.org/10.5194/egusphere-egu2020-12725, 2020.

EGU2020-18391 | Displays | CR3.3

How obstacle geometry and snow properties influence avalanche impact pressure

Michael L. Kyburz, Betty Sovilla, Johan Gaume, and Christophe Ancey

In order to estimate avalanche loads on buildings and structures of various sizes and geometries,  practitioners are interested in recommendations or experimental data for a wide variety of obstacle geometries and sizes. Full-scale avalanche measurements are performed across the world since the late 1970s to increase knowledge about avalanche flow behaviour, including impact on structures. These structures are usually equipped with sensors to measure impact pressure, avalanche velocity and/or snow density. Modifying the structure profile is hardly possible because of high construction costs. To date, it has thus been possible to test and calibrate empirical relationships used in engineering only on a limited number of structures for which experimental data exist. We therefore aim to calibrate the drag coefficient and amplification factor for a broader range of obstacle shapes and sizes. In this context the drag coefficient generalizes the drag coefficient used in Newtonian fluid mechanics when computing the flow past an obstacle. The amplification factor reflects the snow load’s deviation from a hydrostatic-like pressure. To estimate these two parameters, we simulate how an avalanche interacts with differently sized and shaped obstacles using the Discrete Element Method (DEM). First, we test the DEM model’s capacity to reproduce full-scale pressure measurements performed on two different obstacles at the Vallée de la Sionne test site by comparing simulated and measured impact pressures. Second, we run new simulations involving other geometries and dimensions, for which no experimental data exist. Our results show that the pressure distribution depends not only on the obstacle geometry, but also on avalanche flow regime and snow properties. We eventually examine the pressure distribution for different generic geometries and avalanche scenarios. This analysis should ultimately help to improve extant engineering guidelines.

How to cite: Kyburz, M. L., Sovilla, B., Gaume, J., and Ancey, C.: How obstacle geometry and snow properties influence avalanche impact pressure , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18391, https://doi.org/10.5194/egusphere-egu2020-18391, 2020.

EGU2020-22006 | Displays | CR3.3

Relationships between corridor morphological variables and avalanche deposits volumes

Hippolyte Kern, Vincent Jomelli, Nicolas Eckert, and Delphine Grancher

Avalanche deposits cause various types of damage to properties and infrastructures every winter, resulting in significant direct and indirect economic losses. However, the factors controlling the deposit volumes are still largely unknown. The main objective of this study is to analyze the geometric characteristics of avalanche deposits in order to understand their relationships with the avalanche corridors’ morphology in the French Alps. Our study focuses on the analysis of 1491 avalanche deposits spread out over 79 corridor in the upper part of the Haute-Maurienne valley, Savoie department, during the period 2003-2017. This work uses data from the Permanent Avalanche Survey (EPA) database, an inventory of avalanche events occurring at well-known, delineated and mapped corridors in France. A statistical method is used to study the relationships between corridor morphological variables and their associated deposit volumes. Our study area exhibits an mean deposit volume of 17 500m3 (q5% = 4 500 m3 and q95%= 84 000 m3).

Results show that the relationships between corridor morphology and deposit volumes are only significant ( > 0,3 and P < 0,001) for avalanches that occur in winter (November-February). The frequency of snow avalanches also influences the size of the deposits, with the largest deposits observed in corridors that show high annual avalanche frequency. However, avalanche deposit volumes occurring in corridors with a low annual frequency correlate more strongly with the corridor morphology. On the other hand, snow avalanche volumes deposited in spring (March-May) seem to be mostly driven by meteorological variables with almost no correlation with the corridor’s morphology. In more details, deposit volumes are primarily determined by the corridor maximum or mean altitude, which reflects the potential amount of snow that can be mobilized. Corridor slope also exhibit a significant relationship with deposit volumes, which is partially indirect through the effect of the slope on corridors mean annual avalanche frequency. Eventually, surprisingly enough, morphological variables that may intuitively appear as important for deposit volumes such as surface area or orientation are uncorrelated or only poorly correlated with avalanche deposit volumes.

How to cite: Kern, H., Jomelli, V., Eckert, N., and Grancher, D.: Relationships between corridor morphological variables and avalanche deposits volumes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22006, https://doi.org/10.5194/egusphere-egu2020-22006, 2020.

EGU2020-21938 | Displays | CR3.3 | Highlight

Flow-Py: Identifying protection forests and their effects on gravitational natural hazard processes on a regional scale

Michael Neuhauser, Christopher D’Amboise, Michaela Teich, and Jan Thomas Fischer

Recently, strong wind storms have caused large-scale damages in Alpine mountain forests, leaving the underlying infrastructure exposed. These forests often provide protection against gravitational natural hazard processes such as avalanches, rockfall and soil slides. To manage these disturbed forests efficiently and effectively, it is important to know 1) which forest areas serve a protective function to the underlying infrastructure, 2) what is the actual protective effect of these forests on the hazard process, and 3) how one could improve this effect.

To define protective functions and to quantify the protective effects of forests, we created the Flow-Py model that identifies process areas of gravitational hazards, including avalanches, rockfall and debris slides. The model is written in Python to keep it easy adjustable. The run out routine of Flow-Py is based on the principles of energy conservation including frictional dissipation assuming simple coulomb friction, leading to constant travel-angle. Potential release areas and the corresponding travel angle have to be adapted for each type of gravitational mass movements. A important improvement, compared to similar models, is that it can handle mass movement in flat and uphill terrain. One major advantage of this model is its simplicity, resulting in a computationally inexpensive implementation, which allows for an application on a regional scale, covering large simulation areas. The adaptivity of the model further allows to consider existing infrastructure and to detect starting zones endangering the corresponding areas in a back-calculation step. Additionally, by adding forest cover to the simulations we can identify which forest area has a protective function and, based on information about forest structure, calculate the protective effect this forest provides to down slope infrastructure.

Flow-Py is a useful tool to identify forest areas that are important for hazard protection (protective function) and to quantify their protective effect. The model can be applied in protection forest management to prioritize measures in wind throw areas. Furthermore, it is possible to use this tool for analyzing the protective functions and effects of different forest extents and structural conditions, for example, caused by climate change or forest disturbances. In this work we elaborate the potential of Flow-Py by presenting an avalanche case study in the central alpine region of Austria (Gries/Vals, Tyrol, AT). For this case the simulation results indicate a process area affected by avalanches of ~65% with respect to the total area of ~ 195 km².

How to cite: Neuhauser, M., D’Amboise, C., Teich, M., and Fischer, J. T.: Flow-Py: Identifying protection forests and their effects on gravitational natural hazard processes on a regional scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21938, https://doi.org/10.5194/egusphere-egu2020-21938, 2020.

EGU2020-165 | Displays | CR3.3

Impact of land cover on avalanche hazard: how forest cover changes affect return periods and dynamical characteristics simulated by a statistical-numerical avalanche model.

Taline Zgheib, Florie Giacona, Anne-Marie Granet-Abisset, Samuel Morin, and Nicolas Eckert

Land cover and particularly forests have significant impact on snow avalanche initiation and propagation. Mountain forests can prevent avalanche initiation by stabilizing the snow in release areas, and potentially decelerate an avalanche, thus reducing runout distances. Interaction between forests and avalanches is recognized in avalanche modelling mostly by increasing friction parameters. For instance, the dry –Coulomb friction μ of the Voellmy friction law is thought to summarize snow properties, whereas the velocity-dependent friction ξ aims at representing the roughness of the path potentially related to land cover properties. In this work, we hypothesize on the temporal variability of both friction factors, inherited from their dependability on land cover, particularly the forest fraction, namely the aerial percentage of the terrain covered by forests within the extension of the avalanche path. Specifically, we show how the evolution of the forest fraction within the avalanche path affects the return period of runout distances and further dynamical characteristics of simulated avalanches. First, a Bayesian statistical-dynamical model is used to model avalanche frequency and magnitude on the selected path. The two processes are independently modelled, and the joint posterior distribution is estimated using a sequential Metropolis-Hastings algorithm. The forest-avalanche interaction is represented by increasing the total basal friction within the Voellmy friction law (TBF). Accordingly, to increase TBF, the velocity-dependent friction (turbulent friction) ξ is gradually decreased, whereas the dry –Coulomb friction μ is increased. To that end, ξ is assumed to be exponentially decaying with the forest fraction and is modelled as such. The dry –Coulomb friction μ  is assumed to be normally distributed with parameters characterizing its dependency on the release abscissa, mean release depth and the forest fraction. Then, the return period for runout distances and the whole distribution of velocities, flow depths and pressures corresponding to any return periods is computed for different forest fractions representing the true forest evolution within the studied path. Results for a typical avalanche path of the French Alps notably show that, logically, the larger the forest fraction, the higher the return period, but only for runout distances exceeding a given threshold. Future work will include the explicit calibration of the forest cover dependency within the statistical-dynamical approach.

 

How to cite: Zgheib, T., Giacona, F., Granet-Abisset, A.-M., Morin, S., and Eckert, N.: Impact of land cover on avalanche hazard: how forest cover changes affect return periods and dynamical characteristics simulated by a statistical-numerical avalanche model., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-165, https://doi.org/10.5194/egusphere-egu2020-165, 2020.

EGU2020-17597 | Displays | CR3.3

Impacts of land-cover changes on dendrogeomorphic reconstructions of snow avalanches: Insights from the Queyras massif (French Alps)

Adrien Favillier, Robin Mainieri, Jérôme Lopez-Saez, Mélanie Saulnier, Nicolas Eckert, Jean-Luc Peiry, Markus Stoffel, and Christophe Corona

In the course of the 20th century, high-mountain regions, such as the Alps, have experienced a significant warming with temperature increase twice as much as the global average. Such warming strongly alters the cryosphere components. It induces, for example, a shift from solid to liquid precipitation, more frequent and more intense snowmelt phases or a strong decrease in the amount and duration of snow cover, especially at the location of the snow-rain transition. Such changes in snow cover characteristics are expected to induce changes in spontaneous avalanche activity.

On forested stands, dendrogeomorphic analyses provide long and continuous chronologies of snow avalanche events and can thus contribute to the detection of trends potentially related to climate change. However, the non-stationarities found in tree-ring based chronologies of snow avalanches may also be related to socio-environmental changes. In this context, based on the latest the latest developments in dendrogeomorphology, we reconstructed the snow avalanche activity for 6 contiguous paths located in the Grand Bois de Souliers slope (Queyras massif, French Alps) with the aim to :

  1. Detect and illustrate such confounding effects;
  2. Disentangle the trends inherent to tree-ring approaches from real fluctuations in avalanche activity.

The resulting reconstruction covers the period 1750-2016 and evidences two clearly different trends: on the three southern avalanche paths, a sharp increase in the frequency of reconstructed events is observed since the 1970s. The distribution of tree ages, in combination with old topographic maps, allows an attribution of this non-stationarity to the destruction of a large part of the forest stand in the 1910-20s, presumably related to a devastating avalanche event. This extreme event induced a sudden change in the capability of newly colonizing trees to yield dendrogeomorphic records as information on previous or subsequent events has been removed. By contrast, on the three northern paths, snow avalanche activity is truly characterized by a strong reduction since the 1930s related to the progressive afforestation of the paths since the mid-18th century and to the colonization of the release areas since World War 2. Even if we cannot rule out the possibility that global warming may have played a certain, yet likely minor, role in the evolution of these avalanche-forest ecosystem, we conclude that the contrasted evolutions observed between the avalanche paths can, above all, be explained by socio-environmental factors (e.g., forest and grazing management) during the 18th century that have gained in importance by the rural exodus and the abatement of pastoral practices during the 20th century. In that sense, our results evidence quite clearly the crucial need for future studies aimed at detecting changes in mass-movement activity from tree-ring analyses to systematically interpret trends in activity considering interrelations between forest evolution, global warming, social practices and process activity itself.

How to cite: Favillier, A., Mainieri, R., Lopez-Saez, J., Saulnier, M., Eckert, N., Peiry, J.-L., Stoffel, M., and Corona, C.: Impacts of land-cover changes on dendrogeomorphic reconstructions of snow avalanches: Insights from the Queyras massif (French Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17597, https://doi.org/10.5194/egusphere-egu2020-17597, 2020.

EGU2020-11465 | Displays | CR3.3

Automatic high-resolution mapping and classification of avalanche terrain regarding potential release, triggering and run-out zones

Stephan Harvey, Günter Schmudlach, Yves Bühler, Dürr Lukas, Andreas Stoffel, and Marc Christen

Terrain characteristics are one of the main factors contributing to avalanche formation as well as affecting the runout. Hence, terrain assessment is crucial for planning and decision making when travelling in the backcountry. So far, terrain is mainly interpreted manually from topographic maps or by observations in the field. Recent support for interpreting avalanche terrain is given by slope angle layers derived from digital elevation models or the Avalanche Terrain Exposure Scale (ATES) for classifying avalanche terrain manually. While digital elevation models and numerical simulations are used as standard for mapping avalanche hazard threatening settlements and key infrastructure, this is hardly the case when planning tours in the backcountry. Thus, our scope was to classify and map terrain of maximum size class 3 avalanches, which typically threaten backcountry recreationists. We present a new methodology for a high-resolution automatic classification of the avalanche terrain specifically for recreational backcountry travel by taking into account: a) potential avalanche release areas, b) remote triggering of avalanches, c) possible runout zones of max. size 3 avalanches.

Potential release areas were specified by computing a density estimate based on terrain characteristics of observed avalanche starting zones in the Davos region. The potential of remote triggering was estimated with a least-cost path analyses depending on the triggering distance from remotely triggered avalanches. Avalanche runout zones were performed with the avalanche simulation model RAMMS::EXTENDED. Combining all these methods and out of many simulations a classified avalanche terrain map for the entire Swiss Alps and the Jura was created characterizing potential release areas and runout zones. A validation of 870 accidental avalanches in the backcountry of Switzerland shows that only 2% of the mapped avalanche perimeters do not overlap with the simulations. The distribution of the terrain characteristics within both the release areas of the training dataset and the validation data was almost identical. Thus, the extrapolation from the calculated density estimate to the whole of Switzerland is feasible and appropriate. The created map assists the interpretation of avalanche terrain for travelling in the backcountry considering release areas and runout zones. Although the focus is on Switzerland, the methods can also be applied to other mountain areas worldwide.

How to cite: Harvey, S., Schmudlach, G., Bühler, Y., Lukas, D., Stoffel, A., and Christen, M.: Automatic high-resolution mapping and classification of avalanche terrain regarding potential release, triggering and run-out zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11465, https://doi.org/10.5194/egusphere-egu2020-11465, 2020.

EGU2020-8490 | Displays | CR3.3 | Highlight

From Large Scale Hazard Mapping to Risk Assessment

Gregor Ortner, Michael Bruendl, David N. Bresch, and Yves Bühler

Various studies show that changes in the climate system, such as temperature rise and extreme precipitation events strongly influence gravity driven hazards. In 2018, the research programme “Climate Change Impacts on Alpine Mass Movements” began at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL. Within this programme, we develop a framework to model risk caused by climate and socio-economic change. In a first approach, we model avalanche risk in central Switzerland. The changing hazard disposition is modelled with the RAMMS::LSHM Large Scale Hazard Mapping method and risks are assessed with the probabilistic, Python-based risk assessment platform CLIMADA developed at ETH Zurich. We use several hazard scenarios considering different 3-day increases in snow height, an algorithm for determining potential avalanche release areas, a high-resolution terrain model and a forest layer to model the spatial distribution of avalanche hazard for each of the chosen scenarios. The so-derived hazard indication maps are taken as input into CLIMADA to estimate the risk to buildings and infrastructure applying various functions to quantify the avalanche impact.
The result are risk maps which depict spatial and temporal changes of avalanche risk based on various hazard scenarios. The combination with exposure and damageability information, leading to spatio-temporally explicit risk maps provides a comprehensive basis and allows for the appraisal of appropriate risk management options. A risk based approach for lifelines and residential areas will contribute to decision support and highlight adaptations needed for climate change.

How to cite: Ortner, G., Bruendl, M., Bresch, D. N., and Bühler, Y.: From Large Scale Hazard Mapping to Risk Assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8490, https://doi.org/10.5194/egusphere-egu2020-8490, 2020.

CR3.4 – Snow avalanche formation: from snow mechanics to avalanche detection

EGU2020-22435 | Displays | CR3.4

Microstructural insights into the compressive failure of snow based on a peridynamic framework

Jonas Ritter, Henning Löwe, and Michael Zaiser

Highly-porous cohesive granular materials such as snow possess complex modes of failure. Apart from classical failure modes, they show microstructural failure and fragmentation associated with densification within a local, narrow zone. Therefore cracks may form and propagate even under compressive load (‘anticracks’,’compaction bands’). Such failure modes are of importance in a range of geophysical contexts. For instance, they may control the release of snow slab avalanches and influence fracturing of porous rock formations. In the snow context, specific failure mechanisms of the ice matrix and their interplay with the microstructure geometry of snow are still poorly understood. Recently, X-ray computed tomography images have provided insights into snow microstructure and capability of directly simulating its elastic response by the finite element method (FEM). However, apart from thermodynamically driven healing processes the inelastic post-peak behaviour of the microstructure is controlled by localized damage, large deformations and internal contacts. As a result of the well-known limitations of FEM to capture these processes we use Peridynamics (PD) as a non-local continuum method to approach the problem. Due to its formulation, (micro)cracks and damage are emergent features of the problem solution that do not need to be known or located in advance. Furthermore, the Lagrangian character of the governing equations makes the method suitable for simulating large deformations. In this contribution we perform confined uniaxial compression simulations of snow microstructures within a peridynamic framework. Computed tomography images of snow specimen serve as a simulation data base. The obtained results show a novel insight into local failure of snow and allow a better comprehension of the underlying failure mechanisms. This study contributes to improve non-local macroscopic constitutive models for snow for future applications.

How to cite: Ritter, J., Löwe, H., and Zaiser, M.: Microstructural insights into the compressive failure of snow based on a peridynamic framework, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22435, https://doi.org/10.5194/egusphere-egu2020-22435, 2020.

EGU2020-10203 | Displays | CR3.4

Microstructure-based modeling of snow using the material point method and finite strain elastoplasticity

Lars Blatny, Henning Löwe, Stephanie Wang, Chenfanfu Jiang, and Johan Gaume

The mechanical response of snow depends on its microstructural geometry. Parameters such as porosity and orientation (degree of anisotropy) are examples of microstructural parameters that can affect snow mechanical properties. Numerical simulations of snow microstructure obtained from X-ray computer tomography have aided researchers in investigating the elastic response and strength of snow. However, we lack insight into the post-peak and plastic response of snow, which in most previous studies have been oversimplified assuming (quasi-)brittle behavior. We propose studying both the elastic and post-peak behavior using the material point method (MPM), a hybrid Eulerian-Lagrangian continuum numerical method. A major advantage of MPM compared to the (classical) finite element method (FEM) is its ability to handle large deformation processes. Moreover, as a continuum method, it is significantly less computational expensive than the discrete element method (DEM). We independently study the influence of the microstructural parameters on macroscopic quantities, such as elastic modulus, strength, energy release rate and plasticity index, in mixed-mode shear-compression loading simulations. This is accomplished by using the leveled gaussian random field (GRF) approach to generate snow samples with desired microstructural properties. The ice matrix of the microstructure is modeled in the elastoplastic framework with a strain-softening Drucker-Prager failure criterion. Based on the relationships discovered through these numerical experiments, we aim to develop a microstructure-based homogenized constitutive snow model. This study will contribute to improve large-scale snow mechanical models with applications in the simulation of e.g. snow slab avalanche release, avalanche dynamics and snow-tire interaction.

How to cite: Blatny, L., Löwe, H., Wang, S., Jiang, C., and Gaume, J.: Microstructure-based modeling of snow using the material point method and finite strain elastoplasticity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10203, https://doi.org/10.5194/egusphere-egu2020-10203, 2020.

EGU2020-18483 | Displays | CR3.4 | Highlight

Micromechanical modeling of crack propagation in weak snow layer

Gregoire Bobillier, Alec van Herwijnen, Bastian Bergfeld, Johan Gaume, and Jürg Schweizer

Improving the prediction of snow avalanches requires a detailed understanding of the fracture behavior of snow, which is intimately linked to the mechanical properties of the snow layers (strength, elasticity of the weak and slab layer). While the basic concepts of avalanche release are conceptually relatively well understood, understanding crack propagation and fracture propensity remains a great challenge. About 15 years ago, the propagation saw test (PST) was developed. The PST is a fracture mechanical field test that provides information on crack propagation propensity in weak snowpack layers. It has become a valuable research tool to investigate processes and mechanical parameters involved in crack propagation.

Here, we use the discrete element method (DEM) to numerically simulate PST and therefore analyze fracture dynamics based on micromechanical approach. Using cohesive and non-cohesive ballistic deposition, we numerically reproduce the basic required layers for dry-snow avalanche: a highly porous and brittle weak layer covered by a dense cohesive slab.

The results of these numerical PTSs reproduce the main dynamics of crack propagation observed in the field. We developed different indicators to define the crack tip and therefore derive the crack velocity. Our results show that crack propagation on flat terrain reaches a stationary velocity if the snow column in long enough. The length of the snow column to reach stationary crack velocity depends on snowpack parameters. On sloped terrain our results show a transition in the local failure mode, this transition can be visualized from the crack tip morphology and from the main stress component.

Overall, our results lay the foundation for a comprehensive study on the influence of the snowpack mechanical properties on these fundamental processes for avalanche release.

How to cite: Bobillier, G., van Herwijnen, A., Bergfeld, B., Gaume, J., and Schweizer, J.: Micromechanical modeling of crack propagation in weak snow layer , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18483, https://doi.org/10.5194/egusphere-egu2020-18483, 2020.

EGU2020-2409 | Displays | CR3.4

A comprehensive elastic and fracture model for stratified snowpacks

Philipp L. Rosendahl and Philipp Weißgraeber

Dry snow slab avalanche release depends heavily on the stratification of the snow cover and the mechanical properties of the individual snow layers. This does not only concern the depth and condition of the weak-layer but also the ordering and properties of all snow layers above it.

In order to allow for a quick stability assessment of stratified snow covers, we present an analytical model for snow cover deformations, weak-layer stresses and energy release rates of cracks within the weak-layer for arbitrarily layered snowpacks. In particular, the model covers the impact of the layering order on both the extensional and bending stiffness of the slab. It can be used for skier-loaded slopes and for stability tests such as the propagation saw test. The model is highly efficient and readily allows for parameter studies and implementation into other toolchains.

Recognizing weak-layer collapse as an integral part of the fracture process prior to the release of slab avalanches is crucial and explains phenomena such as whumpf sounds and remote triggering of avalanches from low angle terrain. Finite fracture mechanics introduces a new conceptual understanding of crack nucleation. It provides a coupled stress and energy failure criterion for anticrack formation in persistent weak-layers.

Incorporating this physically sound mixed-mode failure criterion, the model allows for the prediction of skier-loads that layered snowpacks can sustain before weak-layer failure triggering is expected that can lead to avalanche release. Our analysis covers the impact of the layering order on weak-layer stresses and critical skier-loads.

How to cite: Rosendahl, P. L. and Weißgraeber, P.: A comprehensive elastic and fracture model for stratified snowpacks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2409, https://doi.org/10.5194/egusphere-egu2020-2409, 2020.

EGU2020-8369 | Displays | CR3.4 | Highlight

Measuring slope-scale crack propagation in weak snowpack layers

Bastian Bergfeld, Alec van Herwijnen, Gregoire Bobillier, and Jürg Schweizer

For a snow avalanche to release, a weak layer has to be buried below a cohesive snow slab. The slab-weak layer configuration must not only allow failure initiation but also crack propagation across a slope. While in the past failure initiation was extensively studied, research focusing on the onset and dynamics of crack propagation only started with the introduction of the Propagation Saw Test (PST), a meter scale fracture mechanical field test. Since then, various studies used particle tracking analysis of high-speed video recordings of PST experiments to gain insight into crack propagation processes and to measure crack propagation speeds. At the slope scale, a few crack speed estimates have been obtained from seismic sensors, videos or visual observation. However, due to experimental limitations, these latter studies can only provide rather crude crack speed estimates and direct comparisons to PST measurements are still missing. Sure, performing experiments in avalanche terrain is challenging and limited for security reasons, but crack propagation occurs also in slopes not sufficiently steep to release an avalanche. This phenomena is called a whumpf. Since crack propagation in whumpfs is presumably similar to that in avalanches, we developed instrumentation to measure crack speeds on artificially triggered whumpfs. We designed small wireless time synchronized accelerometers with a sampling rate of 400 Hz that can be placed on the snowpack. These measure the downward acceleration of the slab when a crack in the weak layer below passes by. Though triggering whumpfs is difficult and unpredictable, we performed a successful experiment with seven sensors placed over a distance of 25 m. Our experiment revealed a crack speed around 50 ms-1. In addition, we obtained very similar crack speed measurements from a 5.3 m long PST carried out close-by (42 ms-1) and a video-based speed estimate of an avalanche triggered two days later (42 – 55 ms-1). Our unique whumpf measurement is the first slope scale speed value that can be directly compared to results obtained with other speed measurement techniques. The similarity between the measured speeds suggests that the one-dimensional crack propagation in PSTs is also similar to the 2-dimensional crack propagation in Whumpfs and real avalanches. PSTs are therefore well suited to investigate crack propagation processes of dry snow slab avalanches.

How to cite: Bergfeld, B., van Herwijnen, A., Bobillier, G., and Schweizer, J.: Measuring slope-scale crack propagation in weak snowpack layers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8369, https://doi.org/10.5194/egusphere-egu2020-8369, 2020.

EGU2020-20604 | Displays | CR3.4

Sharp transition in modes of dynamic crack propagation in dry-snow slab avalanche release

Bertil Trottet, Alec van Herwijnen, Stephanie Wang, Chenfanfu Jiang, Joseph Teran, and Johan Gaume

Dry-snow slab avalanche release can be separated in four distinct phases : (i) failure initiation in a weak snow layer buried below a cohesive snow slab, (ii) onset, (iii) dynamics of crack propagation in the weak layer and eventually (iv) slab release. While a lot has been done to study the first two phases, less is known about dynamic crack propagation and slab release, especially at slope scale. 

In this study, we used the Material Point Method and elastoplasticity to simulate the dynamics of 20 m long centered Propagation Saw Tests (PST). We improved the recent constitutive snow model of Gaume et al. (2018) by developing a new softening law based on the total plastic deformation (volumetric and deviatoric parts) to remove artifacts observed in failure modes.

Interestingly, several regimes of propagations are observed depending on slope angle Θ. For slope angles smaller than the friction angle (Θ < Φ), crack propagates faster in the downslope direction than upslope. The propagation speed increases with slope angle and appears closely related to the bending mechanism which sustains the propagation. For slope angles higher than the friction angle (Θ > Φ), a sharp transition is observed once the crack reaches a critical length lf. We interpret this transition as a change from slab bending to slab tension due to the increasing load in the downslope direction. An estimation of lf is proposed using a basic analytical shear model with residual friction similar to the one developped by McClung in 1979. In this case, the crack propagation speed seems to be mostly related to the P-wave speed in the slab. In this study, we explain the gap between propagation speeds based on 2 m PSTs and some observations of avalanche triggering. Finally, our results show the relevance of shear models which appear sufficient to describe slab avalanche release on steep terrain.

How to cite: Trottet, B., van Herwijnen, A., Wang, S., Jiang, C., Teran, J., and Gaume, J.: Sharp transition in modes of dynamic crack propagation in dry-snow slab avalanche release, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20604, https://doi.org/10.5194/egusphere-egu2020-20604, 2020.

EGU2020-22530 | Displays | CR3.4 | Highlight

Can earthquakes lead to delayed avalanche release ?

Alexander M. Puzrin, Thierry Faug, and Itai Einav

Strong earthquakes often trigger snow avalanches, sometimes with observable delays. Most existing models assume that snow slab avalanches happen simulatenously during or immediatly after their triggering. Therefore, they cannot explain the plausibility of delayed avalanches that are released minutes to hours after a quake. Resolving this shortcoming is critical for improving safety, as emphasized by deadly delayed avalanches in Western Himalaya and, most recently, by the devastating Rigopiano avalanche in Italy’s Abruzzo region, which occurred more than 30 min after the last in a series of major quakes on 18 January 2017. This work establishes the basic mechanism of delays in earthquake-induced avalanche release using a novel analytical model that yields failure scenarios consistent with the Western Himalaya and Rigopiano cases. The mechanism arises from the interplay between creep, strain softening and strain-rate sensitivity of snow, which drive the growth of a basal shear fracture. Our results imply that earthquake-delayed avalanches are rare, yet possible, and could lead to significant damade, especially in long milder slopes. The generality of the model formulation opens a new avenue for exploring other questions related to natural slab avalanche release.

How to cite: Puzrin, A. M., Faug, T., and Einav, I.: Can earthquakes lead to delayed avalanche release ?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22530, https://doi.org/10.5194/egusphere-egu2020-22530, 2020.

EGU2020-22491 | Displays | CR3.4

Changes in the mechanical properties of snow relevant to crack propagation in the hours and minutes following loading

Karl W. Birkland, Bastian Bergfeld, and Alec van Herwijnen

Since most dry slab avalanches occur during or immediately following loading by snowfall or wind deposition, it is important to understand changes in the mechanical properties of the snowpack in the minutes and hours following loading. To investigate these temporal changes we conducted a series of 15 Propagation Saw Test (PST) experiments on a flat, uniform site. The existing snowpack at our site contained a layer of surface hoar buried 2 cm below the snow surface. We used a 5 mm sieve to add 10 cm of snow into a 120 cm by 30 cm cardboard frame and completely isolated our blocks. We then conducted PSTs on the buried surface hoar layer from 4 – 453 minutes after adding the sieved snow. We sprayed dye on the side of our tests and filmed them with a high speed camera at 3000 frames per second. Immediately following our tests we measured the density of the sieved snow, and we collected three SnowMicroPen (SMP) profiles along the length of each PST. In one case we collected SMP data at 10 cm increments along our beam prior to conducing our PST to better assess vertical and lateral variations in slab properties induced by sieving. We utilize Digital Image Correlation analyses of the high speed videos to assess the slab elastic modulus (E), the weak layer specific fracture energy (wf), and the crack propagation speed (c) of each test. All our tests fully propagated to the end of the PST columns. Critical cut lengths (rc) ranged between 1.5 and 9 cm, with rc generally increasing over time, in line with the gradual stiffening of the slab observed in the SMP measurements. Our results provide additional information about the temporal changes of mechanical properties immediately following loading, and will better inform modeling efforts attempting to assess these changes.

How to cite: Birkland, K. W., Bergfeld, B., and van Herwijnen, A.: Changes in the mechanical properties of snow relevant to crack propagation in the hours and minutes following loading, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22491, https://doi.org/10.5194/egusphere-egu2020-22491, 2020.

EGU2020-19589 | Displays | CR3.4

Simulating snow instability in complex terrain

Bettina Richter, Alec van Herwijnen, Mathias W. Rotach, and Jürg Schweizer

Numerical snow cover models are increasingly used in operational avalanche forecasting. While these models can provide snow stratigraphy and some snow instability information, their full potential is not yet exploited in forecasting. We investigated, how well the snow cover model Alpine3D simulated spatial and temporal variations in snow instability. Therefore, simulations were performed in highly varying complex terrain for the winter season 2016-2017 in the region of Davos, Switzerland for an area of about 21 km x 21 km. Alpine3D was forced with data from several automatic weather stations within the region, which were interpolated to a resolution of 100 m. To reproduce observed spatial variability, we scaled precipitation input with snow height measurements derived with airborne laser scanning. For comparison, we also simulated the snowpack without scaling. The simulation with scaling precipitation showed significantly higher spatial variability in modeled snow instability than the simulation without scaling. However, when information was aggregated to aspect and elevation dependent information for the whole region, as it is done for operational forecasting, this variability vanished and scaling precipitation seems unnecessary. At the beginning of the season and towards the end, snow instability depended on aspect, while in the winter months December to March, differences between different aspects were small. The simulations with scaling precipitation revealed a strong influence of snow depth on snow instability, although the various snow instability criteria provided inconsistent results. Simulated profiles, which were classified as rather favourable were rated as rather unstable and vice versa. A comparison to traditional snow profiles shows that snow stratigraphy was reproduced well, but assessing snow instability from stratigraphy alone is not feasible.

How to cite: Richter, B., van Herwijnen, A., Rotach, M. W., and Schweizer, J.: Simulating snow instability in complex terrain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19589, https://doi.org/10.5194/egusphere-egu2020-19589, 2020.

EGU2020-18898 | Displays | CR3.4

Comparing simulated and manual snow profiles to derive thresholds for modeled snow instability metrics

Stephanie Mayer, Alec van Herwijnen, Mathias Bavay, Bettina Richter, and Jürg Schweizer

Numerical snow cover models enable simulating present or future snow stratigraphy based on meteorological input data from automatic weather stations, numerical weather prediction or climate models. To assess avalanche danger for short-term forecasts or with respect to long-term trends induced by a warming climate, the modeled vertical layering of the snowpack has to be interpreted in terms of mechanical instability. In recent years, improvements in our understanding of dry-snow slab avalanche formation have led to the introduction of new metrics describing the fracture processes leading to avalanche release. Even though these instability metrics have been implemented into the detailed snow cover model SNOWPACK, validated threshold values that discriminate rather stable from rather unstable snow conditions are not readily available. To overcome this issue, we compared a comprehensive dataset of almost 600 manual snow profiles with simulations. The manual profiles were observed in the region of Davos over 17 different winters and include stability tests such as the Rutschblock test as well as observations of signs of instability. To simulate snow stratigraphy at the locations of the manual profiles, we obtained meteorological input data by interpolating measurements from a network of automatic weather stations. By matching simulated snow layers with the layers from traditional snow profiles, we established a method to detect potential weak layers in the simulated profiles and determine the degree of instability. To this end, thresholds for failure initiation (skier stability index) and crack propagation criteria (critical crack length) were calibrated using the observed stability test results and signs of instability incorporated in the manual observations. The resulting instability criteria are an important step towards exploiting numerical snow cover models for snow instability assessment.

How to cite: Mayer, S., van Herwijnen, A., Bavay, M., Richter, B., and Schweizer, J.: Comparing simulated and manual snow profiles to derive thresholds for modeled snow instability metrics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18898, https://doi.org/10.5194/egusphere-egu2020-18898, 2020.

EGU2020-8922 | Displays | CR3.4

Potential avalanche release in windthrow areas: the effect of snow height and terrain roughness

Natalie Brožová, Tommaso Baggio, Michaela Teich, Alexander Bast, and Peter Bebi

Windthrow is an important disturbance agent in forest ecosystems and is expected to become more frequent and severe under climate change. Windthrow creates large amounts of surface roughness from downed trees, root plates and stumps. In mountain forests, these elements increase the surface roughness and provide a considerable protective effect against snow avalanches during the first years following a disturbance event. However, if large volumes of snow covers the surface roughness elements, a windthrow area may become prone to avalanche release. Snow accumulation produces terrain smoothing, which is an important factor in avalanche formation.

To assess the effect of snow accumulation on surface roughness in windthrow areas, we quantified terrain smoothing using a vector ruggedness measure and corresponding snow heights, based on digital surface models from summer and winter terrain produced from repetitive UAV flights. Additionally, the snowpack structure was examined using a digital snow micro penetrometer (SMP) to quantify the heterogeneity of snow stratigraphy and to monitor a possible development of weak snow layers over distances greater than 10-20 m, which may contribute to slab avalanche formation. Four study plots were selected to characterize different conditions: i) undisturbed forest, windthrow area with ii) high and iii) low surface roughness, and iv) an open meadow control plot. We then quantified how surface roughness is smoothed depending on the snow height, and at the same time characterized the snowpack structure and the extent of potential weak layers.

We found that increasing snow height leads to decreasing surface roughness, which can produce local release areas. We expect that with continuous increase of snow height, these release areas expand in size; however, further analyses of the snowpack structure will provide deeper insights in potential weak layer formation. Critical conditions for avalanche releases in windthrow areas may thus be defined based on scenarios for snow height and close-range sensing-based roughness data.

How to cite: Brožová, N., Baggio, T., Teich, M., Bast, A., and Bebi, P.: Potential avalanche release in windthrow areas: the effect of snow height and terrain roughness, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8922, https://doi.org/10.5194/egusphere-egu2020-8922, 2020.

Recently, a method applying the Hough Transform was used to obtain the numerical parameters of the shape of the SON section of the spectrograms  of the seismic signals generated by snow avalanches at the experimental site of Vallée de la Sion (VdlS, Valais, Switzerland) (SFL, Davos). The avalanches were of different size and type (powder-snow, transitional and wet-snow) descending along the same path and recorded at two different locations 690 m of distance between them on the path. This helped us to estimate the evolution of the avalanche speed along the path from the starting zone to the run-out zone. We obtained different spectrogram definition parameters according to the type of avalanche.

We apply the same methodology to the seismic signals generated by avalanches at the Ryggfonn experimental site (NGI, Oslo). The avalanches were dry/mixed and dry/dense and occurred in the period (2004-2008). They were recorded in a site along the path. The instrumental conditions, characteristics of the raw data, and the data processing were like those of VdLS. However, the topographic characteristics of the site were different. At the Ryggfonn site, the distance between the starting zone and the sensor was 1640 m (985 in VdlS) and the vertical drop was 800 m (700 m in VdLS).

We present and compare the results obtained to validate a possible application of the method used to VdlS to other places and topographic conditions.

This research was funded by the CHARMA (CGL2013–40828–R) and the PROMONTEC projects (CGL2017-84720-R) of the Spanish Ministry of Economy, Industry and Competitiveness (MINEICO-FEDER) and RISKNAT group (2014GR/1243).

How to cite: Suriñach, E. and Flores-Márquez, E. L.: Comparison of the application of the Hough Transform method (characterization of the SON section in seismic spectrograms) at two different sites (VdlS and Ryggfonn) to study the evolution of avalanches., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8540, https://doi.org/10.5194/egusphere-egu2020-8540, 2020.

EGU2020-13407 | Displays | CR3.4

Seismic localization and dynamical characterization of snow avalanches and slush flows of Mt. Fuji, Japan

Cristina Pérez-Guillén, Kae Tsunematsu, Kouichi Nishimura, and Dieter Issler

Snow avalanches and slush flows are often released at the stratovolcano of Mt. Fuji, which is the highest mountain of Japan (3776 m a.s.l.). These flows represent a major natural hazard as they may attain run-out distances up to 4 km, destroy parts of the forest, and sometimes damage infrastructure. We detected large dimension flows released in the winter seasons of 2014, 2016 and 2018 using the local seismic network installed to monitor the volcanic activity of Mt. Fuji. The maximum detection distance of the seismic network is approximately 15 km for the largest avalanche size class 4–5 (Canadian avalanche classification).  Using data from several seismic sensors, we applied the automated approach of amplitude source location (ASL) based on the decay of the seismic amplitudes with distance to localize and track the avalanche flow paths. We also conducted numerical simulations with Titan2D to reconstruct the avalanche trajectories and thus to assess the precision of the seismic tracking as a function of time, showing mean location errors ranging between 85 and 271 m. The average front speeds estimated from the seismic tracking, which ranged from 27 to 51 m s−1, are consistent with the numerically predicted speeds. In addition, we correlated the source amplitudes and the estimated seismic energies with the approximate run-out distances of the avalanches deduced from the ASL method. The obtained scaling relationships can be useful to empirically classify the flow size. An important task in the near future will be to develop highly effective methods for automatically detecting and tracking avalanche events in the seismic data in near-real time. One approach for the automatization of avalanche detection is the discrimination of seismic sources in the continuous recordings by applying machine learning classification methods. We expect that the precision of the flow tracking could be improved through adaptive weighting of the signals from different stations according to the source–receiver distances and angles.

 

 

How to cite: Pérez-Guillén, C., Tsunematsu, K., Nishimura, K., and Issler, D.: Seismic localization and dynamical characterization of snow avalanches and slush flows of Mt. Fuji, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13407, https://doi.org/10.5194/egusphere-egu2020-13407, 2020.

EGU2020-13993 | Displays | CR3.4

Saltation layer of cohesive drifting snow observed in a wind tunnel

Jean-Luc Velotiana Ralaiarisoa, Florence Naaim-Bouvet, Kenji Kosugi, Masaki Nemoto, Yoichi Ito, Alexandre Valance, Ahmed Ould El Moctar, and Pascal Dupont

Aeolian transport of particles occurs in many geophysical contexts such as wind-blown sand or snow drift and is governed by a myriad of physical mechanisms. Most of drifting particle are transported within de saltation layer and has been largely studied for cohesionless particles whether for snow or for sand. Thus, the theoretical description of aeolian transport has been greatly improved for the last decades. In contrast cohesive particles-air system have received much less attention and there remain many important physical issues to be addressed.  

        In the present study, the characteristics of drifting cohesive snow phenomena is investigated experimentally Several wind tunnel experiments were carried out in the Cryopsheric Environment simulator at Shinjo (Sato et al., 2001). Spatial distribution of wind velocity and the mass flux of drifting snow were measured simultaneously by an ultrasonic anemometer and a snow particle counter. The SPC measures the size of each particle passing through a sampling area. The size is classified into 32 classes between 50 and 500µm. Compacted snow was sifted on the floor. Then snow bed is left for a determined duration time to become cohesive by sintering.Two kinds of snow beds with different compression hardness were used (“hard snow” with a compression hardness of about 60 kPa and “semi hard snow” with a compression hardness of about 30 kPa). Wind tunnel velocity varied from 7 m/s to 15 m/s. Moreover steady snow drifting can be produced by seeding snow particles at a constant rate at the upwind of the test section. The results are compared with those obtained for loose surfaces. It was shown that :

- on hard snow cover, aerodynamic entrainment does not occur and saltating particles from the seeder just rebounded without splashing particles composing the snow surface (Kosugi et al.,2004). b, the inverse of the gradient of the mass flux decay with height is proportional to the friction velocity. The mass flux profiles exhibit a focus point. It is also confirmed (Kosugi et al., 2008) that the saltation height increased with increasing particle diameter throughout the full range of investigated wind tunnel velocity. Such characteristics are not observed for cohesionless snow particles (Sugiura et al.,1998)

-on semi hard snow cover, the inter-particle cohesion makes the transport unsteady and spatially inhomogeneous. A steady state is never obtained. It makes experimental protocol and experiments repeatability tricky. Without seeder, the same trends are observed compared to the previous experiments on hard snow. With seeder, the drifting snow flux dramatically increases, even for low wind speed, leading to snow cover vanish.

How to cite: Ralaiarisoa, J.-L. V., Naaim-Bouvet, F., Kosugi, K., Nemoto, M., Ito, Y., Valance, A., Ould El Moctar, A., and Dupont, P.: Saltation layer of cohesive drifting snow observed in a wind tunnel, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13993, https://doi.org/10.5194/egusphere-egu2020-13993, 2020.

EGU2020-22679 | Displays | CR3.4 | Highlight

The role of surface cohesion in wind-driven snow transport

Francesco Comola, Johan Gaume, Jasper Kok, and Michael Lehning

The wind-driven saltation of sediments, such as snow and sand, is responsible for a wide range of geophysical processes. Blowing-snow, in particular, affects snow surface properties and drives snow redistribution in alpine terrain. As such, it is of fundamental importance for avalanche mechanics. One of the most important controls on initiation and development of snow saltation is the surface cohesion induced by ice particle sintering. Although inter-particle cohesion is known to limit the number of grains lifted from the surface through aerodynamic entrainment and granular splash, the role of cohesion in the development of saltation from onset to steady state is still poorly understood. Using a numerical model based on the discrete element method, we show that saltation over cohesive beds sustains itself at wind speeds one order of magnitude smaller than those necessary to initiate it, giving rise to hysteresis in which the occurrence of transport depends on the history of the wind. Our results further suggest that saltation over cohesive beds requires much longer distances to saturate, thereby increasing the size of the smallest stable bed forms.

How to cite: Comola, F., Gaume, J., Kok, J., and Lehning, M.: The role of surface cohesion in wind-driven snow transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22679, https://doi.org/10.5194/egusphere-egu2020-22679, 2020.

CR4.1 – Evolution of glacial-periglacial-paraglacial landscapes and debris-covered glaciers

EGU2020-19935 | Displays | CR4.1

Geomorphic feedbacks on the moraine record

Leif Anderson and Dirk Scherler

Glacial moraines represent one of the most spatially diverse climate archives on earth. Moraine dating and numerical modeling are used to effectively reconstruct past climate from mountain ranges at the global scale. But because moraines are often located downvalley from steep mountain headwalls, it is possible that debris-covered glaciers emplaced many moraines preserved in the landscape today.

Before we can understand the effect of debris cover on the moraine recored we need to understand how debris modulates glacier response to climate change. To help address this need, we developed a numerical model that links feedbacks between mountain glaciers, climate change, hillslope erosion, and landscape evolution. Our model uses parameters meant to represent glaciers in the Khumbu region of Nepal, though the model physics are relevant for mountain glaciers elsewhere.

We compare simulated debris-covered and debris-free glaciers and their length evolution. We explore the effect of climate-dependent hillslope erosion. We also allow temperature change to control frost cracking and permafrost in the headwall above simulated glaciers. Including these effects holds special implications for glacial evolution during deglaciation and the long-term evolution of mountain landscapes.

Because debris cover suppresses melt, debris-covered glaciers can advance independent of climate change. When debris cover is present during cold periods, moraine emplacement can lag debris-free glacier moraine emplacement by hundreds of years. We develop a suite of tools to help determine whether individual moraines were formed by debris-covered glaciers. Our analyses also point to how we might interpret moraine ages and estimate past climate states from debris-perturbed settings.

How to cite: Anderson, L. and Scherler, D.: Geomorphic feedbacks on the moraine record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19935, https://doi.org/10.5194/egusphere-egu2020-19935, 2020.

EGU2020-18360 | Displays | CR4.1

Post-glacial dynamics of alpine Little Ice Age glacitectonized frozen landforms (Swiss Alps)

Julie Wee, Reynald Delaloye, and Chloé Barboux

Glaciers and frozen debris landforms have coexisted and episodically interacted throughout the Holocene, the former having altered the development, spatial distribution and thermal regime of the latter. In the Alps, the apogee of last interaction phase occurred during the Little Ice Age (LIA). Since then, due to glacier shrinkage, interactions between glaciers and LIA pre-existing frozen debris have gradually diminished and are leaning towards being non-existent. Post-LIA glacier forefields in permafrost environments, including associated glacitectonized frozen landforms (GFL) have shifted from a thermal and mechanical glacier dominant regime towards a periglacial or even post-periglacial regime. GFL are undergoing thermal and mechanical readjustments in response to both the longer-term glacier recession and the more recent drastic climatic warming. They can be expressed by a combination of mass-wasting processes and thaw-induced subsidence.

 

In various regions of the Swiss Alps, slope movements occurring in a periglacial context have been inventoried in previous works using differential SAR interferometry (DInSAR) (Barboux et al., 2014). In the scope of this study, and focusing solely on mass-wasting GFL, the former inventory allowed the identification of the latter under various spatial configurations within LIA glacier forefields. While most observed GFL are disconnected from the associated glacier, some are still connected. Additionally, ground ice occurs as interstitial or massive (buried) glacier ice. This potentially infers the ongoing of non-uniform morphodynamical readjustments.

 

To understand the site-specific behaviour of GFL, the analysis of long-term time-series of permafrost monitoring and multi-temporal high-resolution Digital Elevation Models will allow the assessment of the recent evolution of the Aget and Ritord/Challand LIA glacier forefields (46°00’32’’ N, 7°14’20’’ E and 45°57’10’’ N, 7°14’52’’ E, respectively) and their associated GFL (i.e. push-moraines). Both glacier forefields present a contrasting spatial configuration, making their morphodynamical evolution to differ partly from one another. The Aget push-moraine is a back-creeping GFL, which has been disconnected from the Aget glacier since the 1940s at latest. For the last two decades, surface displacement velocities have decelerated in comparison to the accelerating regional trend (PERMOS, 2019). Additionally, a 30% decrease of the electrical resistivity of the frozen ground, combined with locally observed thaw-induced subsidence of up to 10 cm/year suggest an advanced permafrost degradation. The Ritord/Challand system presents a push-moraine disconnected from its glacier as well as several push-moraines connected to a still existing debris-covered glacier. Between 2016 and 2019, surface lowering up to 10 m attesting massive ice melt has been locally detected in the former where buried glacier ice was visually observed. Whereas in the latter, subtle surface displacements ranging from 10 to 30 cm/year occur. This confirms the heterogeneity of the morphodynamical processes occurring in GFL, expressed as a function of both their spatial configuration and ground ice properties.

 

Barboux, C., Delaloye R. and Lambiel, C. (2014). Inventorying slope movements in an Alpine environment using DInSAR. Earth Surface Processes and Landforms, 39/15, 2087-2099.

PERMOS 2019. Permafrost in Switzerland 2014/2015 to 2017/2018. Noetzli, J., Pellet, C., and Staub, B. (eds.), Glaciological Report (Permafrost) No. 16-19 of the Cryospheric Commission of the Swiss Academy of Sciences, 104.

How to cite: Wee, J., Delaloye, R., and Barboux, C.: Post-glacial dynamics of alpine Little Ice Age glacitectonized frozen landforms (Swiss Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18360, https://doi.org/10.5194/egusphere-egu2020-18360, 2020.

EGU2020-9509 | Displays | CR4.1

Paraglacial adjustment of sediment-mantled slopes through landslide processes in the vicinity of the Austre Lovénbreen glacier (Ny-Ålesund, Svalbard)

Erik Kuschel, Christian Zangerl, Alexander Prokop, Eric Bernard, Florian Tolle, and Jean-Michel Friedt

The climate-induced changes in the high arctic environment influence a wide range of processes, which are rapidly altering the landscape (e.g. glacier retreat, landslide activity). Numerous recent studies are focusing on spatio-temporal characteristics of glacier retreat in the high arctic. However, an exact identification and quantification of landslide processes modifying sediment-mantled slopes in the vicinity of retreating glaciers is in many cases not possible due to the lack of long-term high-resolution spatio-temporal terrain data.

The aim of this study is to investigate terrain changes of sediment-mantled slopes through landslide processes. It focuses on i) the quantitative and spatiotemporal identification of shallow translational debris slides, ii) the failure mechanisms and interaction with a retreating glacier in a high-arctic environment, and iii) the impact of meteorological factors on their formation. The Austre Lovénbreen glacier basin located on the Brøggerhalvøya, Svalbard at 79°N has been chosen to perform these investigations.

Landscape modifications within the basin have been investigated based on: I) high-resolution multi-temporal terrestrial laser scan data (TLS) measured annually from 2012 to 2018; II) images from stationary cameras taken between 2011 and 2018 monitoring the entire basin and; III) two geological field surveys in 2017 and 2018. During the observation period more than 100 distinctive landslide events, with a total volume of approx. 74000 m³ including 84 shallow translational debris slides were identified.

Results clearly show that landslides were the dominant process modifying sediment-mantled slopes during the observation period. Furthermore, deformation and mass waste of these slopes led to the formation of distinctive ice-cored lobate landslide deposits on the glacier. All observed translational debris slides were formed on a distinctive failure surface located at the contact zone between the talus deposits and a subsurface ice layer. Due to the sliding processes, the ice layer was uncovered locally and thus a spatial extension of up to 150 m in elevation above the present-day surface of the Austre Lovénbreen glacier could be verified.

A significant increase in the annual debris slide activity could be observed during the observation period and the data indicates that meteorological factors (e.g. rainfall duration and intensity during the summer, mean annual summer air temperatures and thawing degree days) are the driving factor for landslide activity in the Austre Lovénbreen glacier basin. The impact of these factors is however dependent on the location and exposition of the slopes within the basin. The results presented in this study contribute to a better understanding of adaptation processes of the highly dynamic arctic environments to changing meteorological conditions.

How to cite: Kuschel, E., Zangerl, C., Prokop, A., Bernard, E., Tolle, F., and Friedt, J.-M.: Paraglacial adjustment of sediment-mantled slopes through landslide processes in the vicinity of the Austre Lovénbreen glacier (Ny-Ålesund, Svalbard) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9509, https://doi.org/10.5194/egusphere-egu2020-9509, 2020.

EGU2020-2157 | Displays | CR4.1

Identification of paraglacial and periglacial processes and resulting rockfall activity

Daniel Draebing, Till Mayer, Benjamin Jacobs, and Samuel McColl

Rockfall is characteristic of deglaciated alpine rockwalls. Small (<5 km²) to very small (<0.5 km²) alpine glaciers are located at altitudes where periglacial and paraglacial processes jointly influence rockfall processes. In this study, we (i) reconstruct glacier retreat history, (ii) quantify rock fracture damage, (iii) model permafrost distribution, (iv) model patterns of frost weathering, and (v) assess how these may combine to influence rockfall processes around a small alpine glacier in the Hungerli Valley (Swiss Alps). To achieve this, we use geomorphic, geophysical, geotechnical and remote sensing techniques on three rockwalls (RW1-3) with different glacial retreat history and elevation.

(i) Glacier retreat is reconstructed based on existing LGM ice extent models, mapping of moraines and analysis of historic photos. The resulting retreat history is used as an upper age limit for the calculation of paraglacial rockwall retreat rates.

(ii) Rockwall fracture damage is quantified in the field using laboratory-calibrated seismic refraction tomography and our results demonstrate that rockwall fracture density increases with proximity to the glacier. This relationship suggests that rockwalls in proximity to the glacier are still experiencing paraglacial stress-release jointing and that rockfall is yet to remove these fractured blocks.

(iii) Local permafrost modelling based on temperature logger data indicates that areas with likely permafrost occurrence (<-3°C) are limited to the peaks and upper cirque walls (>3000 m). Areas of ’possible’ permafrost (<0°C) extend to elevations as low as 2700 m.

(iv) We determined rock strength properties in the lab (Draebing and Krautblatter, 2019) and monitored rock temperature in the field for three years. These data were applied to the physical-based frost cracking model by Rempel et al. (2016).  Model simulations show that frost cracking is highly sensitive to lithology and increases with altitude due to decreasing rock temperatures.

(v) We applied terrestrial laserscanning of the rockwalls to quantify rockfall activity. Rockfall volumes demonstrate a typical frequency-magnitude distribution. Applying a space-for-time substitution using glacier retreat history reveals that rockwall retreat rates are increased in proximity to the glacier where rockwalls experience permafrost and a high frost cracking intensity.

In conclusion, our data suggest a synergy of paraglacial processes, frost cracking and permafrost thaw in preparing and triggering rockfalls. This synergy follows an altitudinal gradient that moves upwards with glacier retreat, permafrost thaw and frost cracking trajectories.

 

Draebing, D., & Krautblatter, M.: The Efficacy of Frost Weathering Processes in Alpine Rockwalls. Geophysical Research Letters, 46(12), 6516-6524, 2019.

Rempel, A. W., Marshall, J. A., & Roering, J. J.: Modeling relative frost weathering rates at geomorphic scales. Earth and Planetary Science Letters, 453, 87-95, 2016.

How to cite: Draebing, D., Mayer, T., Jacobs, B., and McColl, S.: Identification of paraglacial and periglacial processes and resulting rockfall activity , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2157, https://doi.org/10.5194/egusphere-egu2020-2157, 2020.

EGU2020-1065 | Displays | CR4.1

Reconstruction of Early Holocene jokulhlaups along the Hvita River and Gullfoss waterfall, Iceland

Greta Wells, Þorsteinn Sæmundsson, Sheryl Luzzadder-Beach, Timothy Beach, and Andrew Dugmore

Glacial lake outburst floods (GLOFs) have occurred across the planet throughout the Quaternary and are a significant geohazard in Arctic and alpine regions today. Iceland experiences more frequent GLOFs—known in Icelandic as jökulhlaups—than nearly anywhere on Earth, yet most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, floods from proglacial lakes may be a better analogue to most global GLOFs.

As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater pooled at ice margins and periodically drained in jökulhlaups. Some of the most catastrophic floods drained from ice-dammed Glacial Lake Kjölur, surging across southwestern Iceland from the interior highlands to the Atlantic Ocean. These floods left extensive geomorphologic evidence along the modern-day course of the Hvítá River, including canyons, scoured bedrock, boulder deposits, and Gullfoss—Iceland’s most famous waterfall. The largest events reached an estimated maximum peak discharge of 300,000 m3 s-1, ranking them among the largest known floods in Iceland and on Earth.

Yet, all our evidence for the Kjölur jökulhlaups comes from only one publication to date (Tómasson, 1993). My research employs new methods to better constrain flood timing, routing, magnitude, and recurrence interval at this underexplored site. This talk presents new and synthesized jökulhlaup geomorphologic evidence; HEC-RAS hydraulic modeling results of flow magnitude and routing; and ongoing geochronological analyses using cosmogenic nuclide exposure dating and tephrochronology. It also situates these events within Icelandic Ice Sheet deglaciation chronology and environmental change at the Pleistocene-Holocene transition. Finally, it examines the Kjölur floods as an analogue to contemporary ice sheet response, proglacial lake formation, and jökulhlaup processes and landscape evolution in Arctic and alpine regions worldwide, where GLOFs pose an increasing risk to downstream communities due to climate-driven meltwater lake expansion.  

Citation: Tómasson, H., 1993. Jökulstífluð vötn á Kili og hamfarahlaup í Hvítá í Árnessýslu. Náttúrufræðingurinn 62, 77-98.

How to cite: Wells, G., Sæmundsson, Þ., Luzzadder-Beach, S., Beach, T., and Dugmore, A.: Reconstruction of Early Holocene jokulhlaups along the Hvita River and Gullfoss waterfall, Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1065, https://doi.org/10.5194/egusphere-egu2020-1065, 2020.

EGU2020-9201 | Displays | CR4.1

Use of Convolution Neural Networks and Object Based Image Analysis for Automated Rock Glacier Mapping

Benjamin Aubrey Robson, Tobias Bolch, Shelley MacDonell, Daniel Hölbling, Philip Rastner, and Nicole Schaffer

Rock glaciers are an important, but often overlooked, component of the cryosphere and are one of the few visible manifestations of permafrost. In certain parts of the world, rock glaciers can contribute up to 30% of catchment streamflow. Remote sensing has permitted the creation of rock glacier inventories for large regions, however, due to the spectral similarity between rock glaciers and the surrounding material, the creation of such inventories is typically conducted based on manual interpretation of remote sensing data which is both time consuming and subjective. Here, we present a method that combines deep learning (convolutional neural networks or CNNs) and object-based image analysis (OBIA) into one workflow based on freely available Sentinel-2 imagery, Sentinel-1 interferometric coherence, and a Digital Elevation Model. CNNs work by identifying recurring patterns and textures and produce a heatmap where each pixel indicates the probability that it belongs to a rock glacier or not. By using OBIA we can segment the datasets and classify objects based on their heatmap value as well as morphological and spatial characteristics and convert the raw probability heatmap generated by the deeo learning into rock glacier polygons. We analysed two distinct catchments, the La Laguna catchment in the Chilean semi-arid Andes and the Poiqu catchment on the Tibetan Plateau. In total, our method mapped 72% of the rock glaciers across both catchments, although many of the individual rock glacier polygons contained false positives that are texturally similar, such as debris-flows, avalanche deposits, or fluvial material causing the user’s accuracy to be moderate (64-69%) even if the producer’s accuracy was higher (75%). We repeated our method on very-high resolution Pléiades satellite imagery (resampled to 2 m resolution) for a subset of the Poiqu catchment to ascertain what difference the image resolution makes. We found that working at a higher spatial resolution has little influence on the user’s accuracy (an increase of 3%) yet as smaller landforms were mapped, the producer’s accuracy rose by 13% to 88%. By running all the processing within an object-based analysis it was possible to both generate the deep learning heatmap and automate some of the post-processing through image segmentation and object reshaping. Given the difficulties in differentiating rock glaciers using image spectra, deep learning offers a feasible method for automated mapping of rock glaciers over large regional scales.

How to cite: Robson, B. A., Bolch, T., MacDonell, S., Hölbling, D., Rastner, P., and Schaffer, N.: Use of Convolution Neural Networks and Object Based Image Analysis for Automated Rock Glacier Mapping, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9201, https://doi.org/10.5194/egusphere-egu2020-9201, 2020.

The landscape of the Tuktoyaktuk Coastlands, western Canadian Arctic is dominated by glacial and geocryological processes that have modified, imprinted and sculpted the surface, depositing surficial materials upon underlying bedrock. Climate warming continues in this region at a rate that is twice the global average, and retrogressive thaw slump (RTS) activity is increasing. Recently, RTS distribution was associated with glacial limits reached by the Laurentide Ice Sheet and corresponding morainal deposits, but RTS are common in other local terrain units. In this glacial-marginal region, permafrost existed pre-glacially, and non-glacial geomorphic processes occurred throughout the Late Quaternary. Superimposed on these conditions are the effects of thermokarst during the Holocene climatic optimum, followed by a period of cooling. Collectively, these processes and associated forms and deposits have contributed variously to preservation, development, or degradation of permafrost and ground ice. The multifaceted Late Quaternary history in this region has impeded understanding of the distributions of ice-cored topography and RTS. For example, rather than glaciogenic ice, the long reigning regional model for ice-cored topography is according to post-glacial development of intrasedimental segregation-intrusion ice. Toward better understanding the evolution of the whole landscape and the distribution of climate-sensitive terrain, we use a landsystems approach as a means to understand how the ice-cored topography developed where RTS form, through analysing the cryostratigraphy. To this end, we identify 6 RTS representing a suite of ice-cored topographic settings, including: (i) preserved basal glacial ice facies within clayey diamict that has been thrusted and folded by glacial push representing morainal deposits of the Sitidgi Stade; (ii) ice contact outwash sediments associated with the Sitidgi Stade, overlying a thermo-erosional contact with underlying basal glacial icy diamict of the Toker Point Stade; (iii) deformed basal glacial ice, eroded down by meltwater-deposited outwash sands some time between the Toker Point and Sitidgi Stades (could be ca. 12.9 kyr BP); (iv) massive, undeformed segregation-intrusion basal ice, likely formed subglacially by freezing of intrasedimental water in pre-existing Pleistocene sands into the base of the glacier, overlain by glacial diamicton;  (v) deformed basal ice facies of intermediate Toker Point – Sitidgi Stades, with an upper layer that may be supra-glacial melt-out till into which segregated ice formed; and (vi) segregation ice that formed as permafrost aggraded into glaciolacustrine clays deposited in proglacial or glacially dammed basins, that was subsequently eroded down by glaciofluvial outwash (Sitidgi Stade). To summarize, the distribution of RTS reflects primarily the distribution of icy basal glacial diamict preserved in moraines, but also basal ice and icy basal diamict that are preserved beneath glaciofluvial deposits, segregation ice in glaciolacustrine deposits, and massive segregation-intrusion ice in Pleistocene sands beneath a till plain.

How to cite: Morse, P., Wolfe, S., and Kokelj, S.: A landsystems approach to understanding the evolution of ice-cored topography and distribution of retrogressive thaw slumps, western Canadian Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12571, https://doi.org/10.5194/egusphere-egu2020-12571, 2020.

EGU2020-17710 | Displays | CR4.1

Quantifying contemporary debris supply in a debris-covered glacier catchment using high-resolution repeat terrestrial LiDAR

Rebecca Stewart, Matthew Westoby, Stuart Dunning, Francesca Pellicciotti, and John Woodward

Glacial debris cover is increasing at a global scale in response to increasing temperatures and negative glacier mass balance. The last decade or so has seen an abundance of research which focuses on debris-covered glacier dynamics and supraglacial processes, such as ice-cliff back wasting and the development of supraglacial ponds. However, far fewer studies have focussed on improving understanding of debris supply to these systems over short- (months-years) or long (centennial-millennial) timescales. Existing work has attempted to quantify headwall erosion by calculating the ratio of supraglacial debris flux (the product of debris thickness and supraglacial velocity) to the headwall catchment area. Whilst these studies provide estimates of headwall erosion rates over long timescales, they are unable to capture subtle (or extreme) spatial and temporal variations in debris supply that operate over shorter timescales. Capturing this variation is important because it will allow predictions of the spatial distribution and volume of debris layers on debris-covered glaciers, which in turn will increase the accuracy of ablation modelling and future melt predictions for these systems. To quantify such variability, we conducted terrestrial LiDAR surveys of potential debris slopes at Miage Glacier, Italy, between July – September 2019. We acquired > 1.8 billion 3D points per catchment survey covering an approximate slope area of 7.7 km2, which supplies debris to ~33% of the glacierised area. Sequential 3D point clouds were co-registered using iterative closest point adjustment. Vegetated surfaces were automatically detected using the CloudCompare plugin CANUPO and removed from further analysis. The M3C2 change detection algorithm was used to calculate 3D change normal to the surface plane, and a 95th percentile confidence interval was applied to eliminate non-significant change. Connected components analysis was used to identify discrete rockfall events, estimate their dimensions, explore their magnitude-frequency and quantify their spatial distribution. We find at least one large failure which developed over a period of two weeks (validated by in situ time-lapse footage) and comprised an estimated volume of around 1 x 106 m3. This particular failure occurred from a recently (<10 years) deglaciated slope, lending support to the theory that large-scale slope response to glacial erosion can be rapid.

How to cite: Stewart, R., Westoby, M., Dunning, S., Pellicciotti, F., and Woodward, J.: Quantifying contemporary debris supply in a debris-covered glacier catchment using high-resolution repeat terrestrial LiDAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17710, https://doi.org/10.5194/egusphere-egu2020-17710, 2020.

EGU2020-382 | Displays | CR4.1

Debris cover growth, ensuing changes in morphology and impact on glacier processes at Pensilungpa Glacier, western Himalaya, India

Purushottam Kumar Garg, Aparna Shukla, Vinit Kumar, and Manish Mehta

Supraglacial debris affects the melting processes and overall response of glaciers to climate change. The present study investigates the temporal variation in debris cover and its influence on the overall state of the Pensilungpa glacier (14.67 ±0.29 km2), western Himalaya, India, which has extensive debris on its lower ablation zone (LAZ). For this, multiple parameters namely length, area, debris extent/thickness, snowline altitude (SLA), surface ice velocity (SIV), surface elevation changes and ice-cliffs were determined using field measurements (2016-2018), GoogleEarth images (2013-2017) and satellite data (Landsat-TM/ETM+/OLI (1993-2017), SRTM (2000) and Terra-ASTER (2017)) to comprehend the past and present status of the glacier. Results show a moderate terminus retreat (6.62 ±2.11 m/y) and area loss (0.11 ±0.03%/y) but a marked slowdown (~50%) in the glacier supported by significant SLA upshift (~6 m/y) during 1993-2017. Geodetic measurements reveal a prominent downwasting of −0.88 ±0.04 m/y during 2000-2017 which is corroborated with ablation-stake measurements that show average annual melting of −0.88 m during 2016-2017 and −1.54 m during 2017-2018. The glacier moved with a slow velocity of 13.94 ±3.94 m/y in 1993/94 and its velocity further slowed-down to 9.33 ±2.76 m/y in 1999/2000 and to 7.63 ±3.87 m/y in 2016/17 revealing a slow-down of 1.97%/y. Notably, the magnitude of change in most glacier parameters was lower in the recent period (2000-2017) as compared to the previous one (1993-2000). The observed SLA upshift (180 m), area loss (0.17 ±0.24%/y) and slowdown rates (4.73%/y) were much higher during 1993-2000. Contrarily, the glacier experienced a low area loss (0.09 ±0.09%/y), slowdown (1.14%/y) and even descend in SLA (43 m) between 2000 and 2017. The overall glacier depletion has resulted in substantial debris cover increase of 2.86 ±0.29%/y during the study period (1993-2017). Following the glacier depletion trend, the debris growth rate was also much higher (6.67 ±0.41%/y) during 1993-2000 and reduced (to 0.81 ±0.12%/y) subsequently (2000-2017). The most recent estimate (2016) shows a total debris cover of 17.35% on the Pensilungpa glacier and field measurements show that the debris tends to be thicker towards the margins. Such a setting probably insulated the glacier margins which, coupled with steady slowdown, has caused the stagnation of the LAZ up to 2 km upstream, which is reflected in SIV results and temporal GoogleEarth images. Also, the debris thickness distribution on glacier is such that it is thicker near the snout (>40 cm) and gradually decreases upstream (<2 cm at ~2.5 km). This has caused differential melting by insulating-effect and albedo lowering-effect and has promoted slope inversion, contributing further to stagnation. Stagnation of the LAZ has caused bulging in the dynamically active upper ablation zone and favored the development of supraglacial lakes (5 in 2017) and numerous ice-cliffs (79 in 2017). In view of insulated margins, back-wasting of ice-cliffs dominates the ablation process which is evident by rapid expansion in their number (48%), perimeter (31%) and area (41%) during 2013-2017. To conclude, the debris cover has significantly altered multiple glacier processes and has largely controlled the glacier evolution.

How to cite: Garg, P. K., Shukla, A., Kumar, V., and Mehta, M.: Debris cover growth, ensuing changes in morphology and impact on glacier processes at Pensilungpa Glacier, western Himalaya, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-382, https://doi.org/10.5194/egusphere-egu2020-382, 2020.

EGU2020-10593 | Displays | CR4.1

A comparison of the drainage systems of two High Asian debris-covered glaciers

Catriona Fyffe, Evan Miles, Marin Kneib, Reeju Shrestha, Rebecca Stewart, Stefan Fugger, Matthew Westoby, Thomas Shaw, Wei Yang, and Francesca Pellicciotti

Debris-covered glaciers are a crucial source of runoff for downstream communities in High Mountain Asia (HMA), especially in dry periods, and knowledge of runoff patterns is important for irrigation and hydropower. However, very few studies have investigated the hydrology of debris-covered glaciers, especially in HMA. Here, debris-covered ice represents about 30% of the total ice mass and is located in the lower reaches where melt dominates. There is increasing evidence that supraglacial debris influences the structure and efficiency of the hydrological system, but dye-tracing studies are rare (only three in HMA) and only one of those attempted repeat traces at different times in the season. Furthermore, previous studies have not sought to examine each of the hydrological components systematically, which is necessary given the unique components of debris-covered glacier drainage systems (e.g. within-debris flow and interlinked pond systems) which are not present on clean glaciers. Finally, there are differences between debris-covered glaciers which may influence their hydrological systems (such as their climate, debris thickness and surface topography), but a lack of consistency between studies hampers clear comparisons. 

This study investigates the hydrological systems of two High Asian debris-covered glaciers with contrasting debris and climate characteristics in both the pre-and post-monsoon. Langtang Glacier in Nepal (visited in May and November 2019) has a very hummocky surface topography covered in metre thick debris, while 24K Glacier, in the SE Tibetan Plateau (visited in June and October 2019) has thinner debris and a particularly wet climate. Our aim was to determine the structure, efficiency and evolution of each part of their hydrological systems. Dye tracing was used to investigate the characteristics of the supraglacial, englacial and subglacial network, and the influence of this drainage network on the resulting runoff was studied using analysis of the proglacial discharge.

The thick debris was an important component of the hydrological system on Langtang Glacier, acting as a source of water in the pre-monsoon and sink of water in the post-monsoon. The supraglacial hydrology of both glaciers had similar characteristics, with clear evidence of hydrological links between supraglacial ponds, composed of flow paths that could cross surface topographical barriers by following englacial or intra-debris routes. On Langtang Glacier the supraglacial hydrology in the post-monsoon became restricted to isolated ponds and streams emanating from ice-cliffs, whereas on 24K Glacier the linked ponds composing the main supraglacial network evolved into a more coherent stream system. Initial analysis suggests that the englacial/subglacial network of Langtang Glacier was inefficient compared to clean alpine glaciers (mean velocity 0.08 ms-1), whereas fast, peaked breakthrough curves on 24K Glacier (mean velocity of 0.5 ms-1 from repeat traces into one moulin) suggest a more efficient system. Debris-covered glaciers therefore share some distinct aspects of their hydrological system (e.g. the occurrence of interlinked ponds), but the englacial/subglacial system efficiency can be altered by the debris thickness, topography and degree of snowcover of the input catchments.

How to cite: Fyffe, C., Miles, E., Kneib, M., Shrestha, R., Stewart, R., Fugger, S., Westoby, M., Shaw, T., Yang, W., and Pellicciotti, F.: A comparison of the drainage systems of two High Asian debris-covered glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10593, https://doi.org/10.5194/egusphere-egu2020-10593, 2020.

EGU2020-976 | Displays | CR4.1

Structure and englacial debris content of a Himalayan debris-covered glacier revealed by an optical televiewer

Katie Miles, Bryn Hubbard, Duncan Quincey, Evan Miles, and Ann Rowan

Himalayan debris-covered glaciers contribute to the discharge of some of Earth’s largest river systems, shaping the seasonal water supply to millions of people. The supraglacial debris layer heavily influences the pattern of surface melt, producing a range of unique surface features that make it challenging to collect any data, particularly from the interior of such glaciers. Models of debris-covered glaciers therefore lack calibration and validation data, which are needed for accurate predictions of future glacier geometric change and contributions to river discharge, water resources and ultimately sea level. In 2017 and 2018, we logged four boreholes drilled using pressurised hot water into the debris-covered Khumbu Glacier, Nepal Himalaya, with a high-resolution optical televiewer. The boreholes were located at four sites across the lower glacier’s debris-covered area, down-flow of the Khumbu Icefall. The resulting logs, ranging in length from 22–150 m, produced a 360° geometrically-accurate full-colour image of each borehole at ~1 mm vertical and ~0.22 mm (1,440 pixel) horizontal resolution. The logs reveal three material facies: i) steeply-dipping ice layers, some including debris; ii) steeply-dipping sediment-rich layers; and iii) clusters of sediment and debris dispersed through the ice. On the basis of these facies, we present reconstructions of the glacier’s structure and historical flow paths and the first measurements of the englacial debris concentration of a Himalayan debris-covered glacier. From the latter, we additionally infer both the sources of this englacial debris and of the supraglacial debris layer present across much of the lower ablation area of Khumbu Glacier.

How to cite: Miles, K., Hubbard, B., Quincey, D., Miles, E., and Rowan, A.: Structure and englacial debris content of a Himalayan debris-covered glacier revealed by an optical televiewer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-976, https://doi.org/10.5194/egusphere-egu2020-976, 2020.

EGU2020-20006 | Displays | CR4.1

Characteristics and interannual changes of ice cliffs on the debris-covered glaciers of HMA

Marin Kneib, Evan Miles, Pascal Buri, and Francesca Pellicciotti

Ice cliffs have been shown to be key contributors to the mass balance of debris-covered glaciers in High Mountain Asia. They are zones of enhanced energy inputs and contribute to glacier melt 3 to 15 times more than the surrounding debris, with backwasting rates of up to 10 cm/day. Field observations have shown that these features can evolve quickly, extending by 50% of their area or being entirely reburied by debris within the course of one monsoon season, while others remain stable over several years. They can also appear suddenly via abrupt events such as englacial conduit collapse, crevasse opening or slope destabilization by supraglacial streams or ponds. These mechanisms and evolution patterns have never been quantified nor even observed at the scale of a glacier, mainly because very few repeat datasets of appropriate temporal resolution exist.

Here we combine one existing and new multi-temporal datasets of cliff outlines derived manually or semi-automatically, from debris-covered glaciers in four regions of HMA with varying topography, debris-cover and climatic regimes. We use a tracking algorithm to automatically detect the evolution of these features over several years, focusing on their formation rates and the evolution of their shapes and sizes obtained from high resolution digital elevation models. Surface velocity maps, debris thickness measurements and outlines of ponds and the main supraglacial streams are used to relate the evolution patterns to glacier dynamics and supraglacial hydrology.

We follow and analyze the inter-annual evolution of more than one thousand cliffs along with the nearby ponds. These results allow us to propose a classification of ice cliffs based on the mechanisms governing their genesis and evolution. Finally, we use this classification to map and quantify the different genesis mechanisms dominant at each of the four sites. By considering the evolution of each cliff independently, this study bridges the gap between large-scale statistical studies of cliff populations and detailed field observations focusing on a few features of specific glaciers. In addition to improving our general understanding of ice-cliff evolution, this study provides the first consistent and regional dataset of cliff characteristics, changes and patterns to support modeling of ice cliffs at a large scale.

How to cite: Kneib, M., Miles, E., Buri, P., and Pellicciotti, F.: Characteristics and interannual changes of ice cliffs on the debris-covered glaciers of HMA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20006, https://doi.org/10.5194/egusphere-egu2020-20006, 2020.

EGU2020-5057 | Displays | CR4.1

Satellite remote sensing of ice cliff migration

Bas Altena and Andreas Kääb

Ablation patterns on debris-covered glaciers are highly complex and spatially variable, while accessibility is complicated due to steep topography and loose surface debris material. One of the main ablation components on debris-covered glaciers is ice melt on steep ice cliffs and associated cliff migration. When using measurement techniques that operate in absolute coordinates, a main challenge is to separate cliff retreat from the underlying ice movement. In-situ measurements are spatially limited, while giving highly detailed understanding of processes occurring on individual ice cliffs. Drones can extent such detailed measurements to a whole glacier tongue, but are still limited to a few glaciers and measurement times. Here we show how measurements of cliff migration rates towards a regional scale are possible with spaceborne optical instruments. For this study we focus on the Mt. Everest region, specifically the Khumbu Glacier and other glaciers in the surrounding. We use Venμs, a French-Israeli multi-spectral satellite, that provides images at high temporal resolution (a two day repeat), and at high spatial resolution (5m), at this spatial resolution it provides sufficient detail to investigate individual ice cliffs.

Migration of ice cliffs can have a dominant direction, but their shape evolves over time, complicating pattern matching. Similar challenges occur for velocity extraction of the underlying glacier ice, where the shadow casted by ice cliffs is a dominant feature on glacier imagery, thus instead of debris patterns, the velocity estimates have ice cliff migration patterns within. Hence, in order to reduce the interference between both processes we reduce the influence of shadow within the imagery and extract bulk glacier ice velocity. While specific ice cliff features are isolated and tracked. Thus different image tracking techniques are deployed, in order to distinguish one displacement from the other.

The ice-cliff migration can be separated from the general glacier velocity, which results in a regional estimate of ice cliff back wasting, and thus a proxy for clean ice mass-balance of debris-covered glaciers from space. Venμs is a demonstrator satellite, with a limited lifetime and acquisition strategy, but our automatic methodology is generic and can be transferred to, for example, the 10m imagery from Sentinel-2, making regional analysis feasible.

How to cite: Altena, B. and Kääb, A.: Satellite remote sensing of ice cliff migration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5057, https://doi.org/10.5194/egusphere-egu2020-5057, 2020.

EGU2020-8475 | Displays | CR4.1

Improving geomorphological process understanding of complex glacier surfaces using aerial robotics

Matt Westoby, David Rounce, Thomas Shaw, Catriona Fyffe, Peter Moore, Rebecca Stewart, and Ben Brock

In the last decade or so, improvements in unpiloted aerial systems (UAS) technology and the emergence of low-cost digital photogrammetry have democratised access to accurate, high-resolution topographic data products, particularly in remote, glacial environments. One such application of these tools has been for advancing understanding of debris-covered glaciers (DCG) which are an important component of the high-mountain cryosphere, but also where detailed, ground-based process analysis is challenging. In this work, we seek to improve meso-scale (<km) geomorphological understanding of DCG surface evolution over multi-annual timescales by quantifying how debris moves around on the surface of these glaciers, and how debris transport is reconciled with wider patterns and mechanisms of ice mass loss. We applied annual UAS-photogrammetry and DEM differencing alongside debris thickness and debris stability modelling to unravel the evolution of a 0.2 km2 sub-region of the debris-covered Miage Glacier, Italy, between June 2015 and July 2018. Following corrections for glacier flow, DEM differencing revealed widespread surface lowering (mean 4.1 ± 1.0 m a-1; maximum 13.3 m a-1). We combined DEMs of difference with local meteorological data and a sub-debris melt model to produce high resolution (metre-scale) maps of debris thickness. Median debris thicknesses ranged from 0.12 – 0.17 m and were highly spatially variable. Debris thickness differencing revealed localised debris thinning across ice cliff faces, except those which were decaying, where debris thickened, as well as ingestion of debris by a newly exposed englacial conduit. Debris stability mapping showed that 18.2 - 26.4% of the survey area was theoretically subject to debris remobilisation in a given year. By linking changes in stability to changes in debris thickness, we observed a net debris thinning signal across slopes which become newly unstable, and a net thickening signal across those which stabilise between years. Finally, we linked morphometric descriptors of the glacier surface with debris thickness change data to derive empirical relationships which describe observed rates of downslope debris thickening as a function of slope-distance and slope angle. These UAS-enabled data provide new insight into mechanisms and rates of debris redistribution on glacier surfaces over sub-decadal timescales, and open avenues for future research to explore patterns of debris remobilisation and the morphological evolution of glacier surfaces at much larger spatiotemporal scales.

How to cite: Westoby, M., Rounce, D., Shaw, T., Fyffe, C., Moore, P., Stewart, R., and Brock, B.: Improving geomorphological process understanding of complex glacier surfaces using aerial robotics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8475, https://doi.org/10.5194/egusphere-egu2020-8475, 2020.

EGU2020-17912 | Displays | CR4.1

Geomorphological mapping of an alpine rock glacier with multi-temporal UAV-based high density point cloud comparison

Francesca Bearzot, Roberto Garzonio, Biagio Di Mauro, Umberto Morra Di Cella, Edoardo Cremonese, Paolo Pogliotti, Paolo Frattini, Giovanni B. Crosta, Roberto Colombo, and Micol Rossini

The acquisition of high-resolution topographic data is a widely used tool for studies related to the processes and dynamics of the Earth's surface. In this work, we present the results of the repeated acquisition of photogrammetric data by Unmanned Aerial Vehicle (UAV) in order to detect the topographic evolution of an alpine rock glaciers located in Valtournenche (AO, Italy). Field monitoring conducted in recent years has shown significant variations in the behaviour of these landforms, with an increasing trend of their dynamism, raising questions about their stability in changing climatic conditions.

 

The photogrammetric shots were taken with a DJ Phantom 4 UAV equipped with a compact RGB digital camera. The acquisitions were performed yearly from 2012 up to 2019 with a ground sampling distance never exceeding 5 cm/px. Contemporary to the acquisitions, approximately 20 Ground Control Points were placed on the rock glacier and on the surrounding areas and their coordinates were measured with a differential GPS (dGPS) for georeferencing UAV images. Moreover, in 2014, 2015 and 2019 geophysical campaigns were carried out for the detection of ice lenses under the debris cover of the rock glacier.

 

Structure-from-motion techniques were applied on overlapping images to create high-density point clouds, than converted in orthophotos and digital surface models of the Earth’s surface.

The point clouds were analysed using the M3C2 (Multiscale Model to Model Cloud Comparison) plug-in, freely available in the CloudCompare software. Maps of surface changes between acquisition pairs in the period from 2015-2019 have been created. The comparison allowed the identification of "material supply" and "material removal" zones, slightly variable from one year to the next. The major accumulation zones are concentrated along the frontal sector of the rock glacier, more focused on the western sector (black lobe) and secondly on the right side of the rock glacier (white lobe). The removal of material is mainly concentrated on the higher altitude of the body but also in correspondence to the systems of crevasses and scarps and on the central part of the black lobe.

The surface displacement analysis of the rock glacier was also performed selecting manually several clearly identifiable features on the orthomosaics collected. Blocks and ridges-and-furrows complex were marked on the 2019 orthomosaic and found them on the 2015 orthomosaic. This approach allows improving and quantifying the dynamics of the different portions of the individual apparatus.

The velocity fields’ patterns highlight non-homogeneous displacements between the West (black lobe) and East part (white lobe) of the whole rock glacier. Specifically, the black lobe showed an average horizontal displacement of around 1 m/y while the white lobe moved significantly slower than the previous one (approximately 0.5 m/y). Overall, the rock glacier moved downslope at an average horizontal velocity of 0.60 m/y in the frontal tongue, 0.48 m/y in the central portion and 0.30 m/y in the upper zone.

How to cite: Bearzot, F., Garzonio, R., Di Mauro, B., Morra Di Cella, U., Cremonese, E., Pogliotti, P., Frattini, P., B. Crosta, G., Colombo, R., and Rossini, M.: Geomorphological mapping of an alpine rock glacier with multi-temporal UAV-based high density point cloud comparison, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17912, https://doi.org/10.5194/egusphere-egu2020-17912, 2020.

EGU2020-10373 | Displays | CR4.1

60 years of rock glacier displacements and fluxes changes over Laurichard Rock glacier, French Alps.

Diego Cusicanqui, Antoine Rabatel, and Xavier Bodin

Recent acceleration of rock glaciers has been largely documented in the European Alps, hence highlighting an increase in flow speed of stable rock glaciers and some anomalous behaviors called destabilization (development of landslides-like features on the rock glacier surface).  In this study, we focus on Laurichard active rock glacier, 225 m long, up to 75 m wide, which covers an area of 0.084 km2 and has the longest measurement time-series in the French Alps. Here we aim to understand the causes of the changes in ice velocity of Laurichard rock glacier. We investigate the changes in the fluxes of ice masses across longitudinal and transversal profiles in order to be able to analyze in details the differences between the upper part and the front of the glacier. Using a combination of remote sensing data from 1952 (historical aerial images) until 2018 (Pléiades high-resolution satellite images), we documented the three-dimensional evolution of the Laurichard rock glacier during the last 60 years. We calculated the surface flow velocity between 1952 and 2018 using a feature-tracking algorithm at a resolution of 1 m and a precision of 0.5 m. Digital elevation models were assembled using the SfM techniques for aerial images, and the AMES stereo pipeline for Pléiades data. In addition, we made the analysis using in-situ annual velocities and temperatures data allowing to understand better which factors mostly explain the kinematic behavior.  We reconstructed a time series of changes in surface elevation by systematically co-registering and differencing DEMs between 1952 and 2018, with an average precision of 1 m. We first observed that the average annual horizontal velocity measured had increased progressively from 0.65 m yr-1 to 1.1 m yr-1 to 1.5 m yr-1 for the periods 1952-1960, 1994-2003 and 2013-2018, respectively. On the other hand, the surface mass changes and long term monitoring of mass transport show for all analyzed periods a clear negative surface elevation change of 2 m on average, between 1952 and 2018. The area with most of the elevation changes is the frontal part of the glacier, which is consistent with the increase in speed, which represents a mass exchange from the upper part to the front. We conclude that the rates of rock glacier mass transport have increased during the last 20 years and hypothetize, for this rock glacier, a transition state controlled mainly by local topographical factors which will eventually lead to high speed rock glacier or rock glacier destabilization.

How to cite: Cusicanqui, D., Rabatel, A., and Bodin, X.: 60 years of rock glacier displacements and fluxes changes over Laurichard Rock glacier, French Alps., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10373, https://doi.org/10.5194/egusphere-egu2020-10373, 2020.

EGU2020-1605 | Displays | CR4.1

Creating a rock glacier inventory of the northern Nyainqêntanglha range (Tibetan Plateau) based on InSAR time-series analysis

Eike Reinosch, Johannes Buckel, Markus Gerke, Jussi Baade, and Björn Riedel

The northern Nyainqêntanglha range on the southern Tibetan Plateau reaches an elevation of 7150 m and is mainly characterized by a periglacial landscape. A monsoonal climate, with a wet period during the summers and arid conditions during the rest of the year governs the landscape processes. Large parts of the mountain range are considered permafrost due to the high altitude and the associated low air temperature. Rock glaciers, which are bodies of ice-rich debris, are a typical landform. The recently published IPCC report on the cryospheres of high mountain areas highlights the sensitivity of rock glaciers to climate warming and emphasizes the importance of their study.

We study the distribution of rock glaciers of the northern Nyainqêntanglha range and our aim is to produce an inventory of active rock glaciers based on their surface motion characteristics. The lack of higher order vegetation and the relatively low winter precipitation enable us to employ Interferometric Synthetic Aperture Radar (InSAR) time-series techniques to study both seasonal and multi-annual surface displacement patterns. InSAR is a powerful microwave remote sensing technique, which makes it possible to study displacement from a few millimeters to centimeters and decimeters per year. It is thus suitable to detect sliding and creeping processes related to periglacial landscapes and permafrost conditions on the Earth’s surface. We use both Sentinel-1 (2015-2019) and TerraSAR-X ScanSAR data (2017-2019) for our analysis.

In this study we differentiate rock glaciers from the surrounding seasonally sliding slopes by their significantly higher surface creeping rates with mean velocities of 5–20 cm yr-1. We also observe that the velocity of rock glaciers is less dependent on the summer monsoon, which allows us to further differentiate between rock glaciers and other landforms. This method could potentially be used to create rock glacier inventories in other remote regions, as long as the snow cover in winter is thin enough to allow continuous InSAR time-series analysis. These rock glacier inventories are necessary to assess the effects of climate change on vulnerable high mountain regions.

How to cite: Reinosch, E., Buckel, J., Gerke, M., Baade, J., and Riedel, B.: Creating a rock glacier inventory of the northern Nyainqêntanglha range (Tibetan Plateau) based on InSAR time-series analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1605, https://doi.org/10.5194/egusphere-egu2020-1605, 2020.

EGU2020-8159 | Displays | CR4.1

Pushing the limits of electrical resistivity tomography measurements on a rock glacier at 5500 m a.s.l. on the Tibetan Plateau: Successes and Challenges

Nora Krebs, Anne Voigtländer, Matthias Bücker, Andreas Hördt, Ruben Schroeckh, and Johannes Buckel

Geophysical methods provide a powerful tool to understand the internal structure of active rock glaciers. We applied Electrical Resistivity Tomography (ERT) to a rock glacier at an elevation of 5500 m a.s.l. in the semi-arid Nyainqêntanglha mountain range on the Tibetan plateau, China.  The investigations comprised three transects across the rock glacier and its catchment, each spanning over a distance of 296 m up to 396 m, equipped with 75 up to 100 electrodes respectively. Our measurements were successful in revealing internal structures of the rock glacier, but were also accompanied by challenges.

We successfully detected first-order permafrost structures, such as a shallow about 4 m thick active layer of low electrical resistivity values that was underlain by potentially ice rich zones of high resistivity. Further high-resistivity zones were found and interpreted as dense bed rock of adjacent slopes that undergird the loose rock glacier debris.

Challenges, we faced in the application of ERT, were mainly posed by the morphology and internal structure of the rock glacier itself. Coarse debris created a rough surface that prevented a uniform setup with accurate 4 m spacing. The presence of loosely nested blocks of pebble size up to boulders with large interspaces resulted in high contact resistances. The consequent low injection current densities and possible noisy voltage readings downgraded part of the data, causing low data density and resolution. Coupling was partly improved by attaching salt-watered sponges to the electrodes and adding more conductive fine-grained materials to the electrodes. The detected high resistivity ice layer impeded deep penetration of electrical currents, which caused that the lower limit of the permanently frozen zone could not be defined.

Despite these challenges, the captured ERT profiles are an indispensable contribution to the sparse field data on the internal structure of rock glaciers on the Tibetan plateau. Our results contribute to a better understanding of the prospective evolution of rock glaciers in dry, high mountain ranges under a changing climate.

How to cite: Krebs, N., Voigtländer, A., Bücker, M., Hördt, A., Schroeckh, R., and Buckel, J.: Pushing the limits of electrical resistivity tomography measurements on a rock glacier at 5500 m a.s.l. on the Tibetan Plateau: Successes and Challenges , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8159, https://doi.org/10.5194/egusphere-egu2020-8159, 2020.

EGU2020-7266 | Displays | CR4.1

What makes a rock glacier? Insights into the structure and dynamics of an active rock glacier on the Tibetan Plateau

Johannes Buckel, Eike Reinosch, Nora Krebs, Anne Voigtländer, Michael Dietze, Ruben Schroeckh, Matthias Bücker, and Andreas Hördt

Rock glaciers are typically regarded as periglacial features and their dynamics are supposed to be driven by ice content. Under ongoing global warming we expect these structures and dynamics to change and at least decay. This would be especially the case of rock glaciers in climate-sensitive high mountains of the Tibetan plateau, like in the Nyainqêntanglha range. Despite the similar past and present periglacial climatic conditions in this region, rock glaciers are only formed in a few, specific valleys. With this study, we aim to provide insights into the environmental conditions under which rock glaciers are formed and maintained, to be able to better understand how they will respond to changing boundary conditions, imposed by global warming.

To assess “what makes a rock glacier?” we studied such a feature in the Qugaqie basin, at 5500 m a.s.l. To describe the structure and the dynamics of this active rock glacier we applied several methods (geomorphological mapping, geophysics, remote sensing) and we incorporated catchment area properties such as geology, water and sediment sources. Mapping of the geomorphology, the geology and surface material properties characterizes the external structure of the rock glacier. The internal structure, like the active layer zone and the existence of ice, is described by electrical resistivity tomography (ERT). To investigate the surface dynamics of the rock glaciers, we quantify displacement rates using Interferometric Synthetic Aperture Radar (InSAR) time-series analysis. To gain insight to internal deformation dynamics we use environmental seismology, allowing for detection and location of crack signals within the rock glacier. The seismic network also allows tracking rock falls at the head scarp and continuously monitoring glaciofluvial patterns. We find that the singularity of the presence of the studied rock glacier is most likely related to a specific melange of the geological structures, former glaciation of the valley, catchment size and shape and especially water availability.

How to cite: Buckel, J., Reinosch, E., Krebs, N., Voigtländer, A., Dietze, M., Schroeckh, R., Bücker, M., and Hördt, A.: What makes a rock glacier? Insights into the structure and dynamics of an active rock glacier on the Tibetan Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7266, https://doi.org/10.5194/egusphere-egu2020-7266, 2020.

EGU2020-19637 | Displays | CR4.1

Occurrence and characteristics of ice-debris landforms in Poiqu basin (central Himalaya)

Tobias Bolch, Philipp Rastner, Jan Bouke Pronk, Atanu Bhattacharya, Lin Liu, Yan Hu, Guoqing Zhang, and Tandong Yao

Rock glaciers and other ice-debris landforms (I-DLs) are an important part of the debris-transport system in high mountains and their internal ice could provide a relevant contribution to water supply especially in dry regions. Recent research has shown that I-DLs are abundant in High Mountain Asia, but knowledge about their occurrence and characteristics is still limited.

We are therefore investigating I-DLs in the Poiqu basin (~28°17´N, 85°58´E) – central Himalaya/southern Tibetan Plateau using remote sensing aided by field observations. We use very high-resolution stereo Pleiades data from the contemporary period and stereo Corona and Hexagon data from the 1970s to generate digital elevation models, applied satellite radar interferometry based on ALOS-1 PALSAR and Sentinel-1 SAR data and feature tracking using Sentinel-2 and the Pleiades data. Generated DEMs allowed us to create a hillshade to support identification, to derive their topographical parameters and to investigate surface elevation changes. I-DLs were identified and classified based on their characteristic shape, their surface structure and surface movement. Field observationssupported the identification of the landforms.

We found abundant occurrence of rock glaciers (with typical characteristics like lobate-shaped forms, ridges and furrows as well as steep fronts) but also significant movements of both former lateral moraines and debris-slopes in permafrost area. Preliminary results revealed the occurrence of more than 350 rock glaciers covering an area of about 21 km2. About 150 of them are active. The largest rock glacier has an area of 0.5 km2 and three have an area of more than 0.3 km2. The rock glaciers are located between ~3715 m and ~5850 m with a mean altitude of ~5075 m a.s.l.. The mean slope of all rock glaciers is close to 17.5° (min. 6.8°, max. 37.6°). Most of the rock glaciers face towards the Northeast (19%) and West (18.5%). Surface elevation changes between the 1970s and 2018 show no significant changes but indicate slight elevation gain at the front of active rock glaciers caused by their downward movements.

Work will be continued to generate an inventory of all I-DLs in the study area including information about their activity and surface elevation changes.

How to cite: Bolch, T., Rastner, P., Pronk, J. B., Bhattacharya, A., Liu, L., Hu, Y., Zhang, G., and Yao, T.: Occurrence and characteristics of ice-debris landforms in Poiqu basin (central Himalaya), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19637, https://doi.org/10.5194/egusphere-egu2020-19637, 2020.

Contemporary climate warming in the Arctic affects the dynamics of the entire environment, including components of the cryosphere: permafrost and glacier systems. The change in the structure of the polar landscape since the termination of the Little Ice Age (ca. 1900) was expressed by widespread retreat of glaciers, progressive exposure of glacial landforms at ice margins and opening ice marginal zones to increasing paraglacial and periglacial processes operating synchronously in adjacent areas.

The main aim of the presented study was to determine the course and spatial diversity of landscape transformation in the Sørkapp Land peninsula (Spitsbergen) as a result of glacier recession in the periods 1961-1990-2010 based on existing remote sensing data. Using photogrammetric methods of data processing combined with GIS techniques, the rates of proglacial and ice-marginal terrain change following deglaciation have been determined.

For the mentioned research period, the area of the marginal zones almost doubled from 53 km² to 99 km². The dynamics of landscape transformation in these zones manifested in rapid reduction in the surface elevation of ice-cored moraines (with mean decrease of 0,18-0,22 m per year) and the forms underlain by the dead-ice. This process was enhanced by mass movements and debris flows. Within marginal zones, the area of subglacial landforms and sediments increased by 31 km² from 8 km² in 1961 to 39 km² in 2010.

Larger volume of proglacial waters and associated intensification of denudation, transport and accumulation of sediments entailed area increase of sandurs and proglacial riverbeds (which almost tripled from 3,5 km² to over 10 km²). Further redeposition and remobilization of material in some places also promoted enhanced sediment aggradation in coastal environment forming new beaches and spit systems.

How to cite: Dudek, J. and Strzelecki, M. C.: Post-Little Ice Age retreat of glaciers triggered rapid paraglacial landscape transformation in Sørkapp Land (Spitsbergen) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8967, https://doi.org/10.5194/egusphere-egu2020-8967, 2020.

EGU2020-17195 | Displays | CR4.1

Paraglacial Cirque Headwall Instability - Regional Scale Assessment Of Preconditioning Factors

Andreas Ewald and Jan-Christoph Otto

Cirques are characteristic landforms in high alpine environments with flat cirque floors flanked by steep headwalls. From a rock-mechanical perspective, rock walls are assumed to adjust over time according to their internal rock mass strength, which is determined by a number of factors including e. g. intact rock strength and fracture system characteristics. However, temperatures permanently below freezing as well as glacier coverage keep cirque headwalls stabilised so that slope inclination can evolve during glaciation that is far beyond strength equilibrium. When cirque headwalls deglaciate, the relative importance of rock mass properties increases drastically as they precondition rock slope instability. Cataclinal headwalls, where major fracture sets dip out of the slope, are rated as unstable and usually respond rapidly to glacier retreat. Anaclinal headwalls with in-dipping fracture sets in contrast respond delayed and probably less drastically. To date, a systematic assessment of the predisposition of cirque headwalls for rock slope instability following deglaciation is lacking. We aim to tackle this lacking by a systematic regional analysis of predisposition factors using GIS tools.

 

For the central Hohe Tauern Range, Austria, regional datasets are available for the most important preconditioning factors including topography (digital elevation model), geology (digital geological map), glacier extent (digital glacier inventory), and permafrost distribution (PERMAKART 3.0). We combined geomorphometric analyses with geotechnical data to locate and evaluate the sensitivity of glacier headwalls to rock slope instability using GIS and object-based analysis techniques.

 

Our results show that a vast majority of the headwalls identified can be divided by a significant convexity in the slope profile curvature into a larger, upper and a lower, steeper headwall section (> 60°). The lower limit of the steeper section is marked by a significant concavity in the slope profile curvature, which is commonly known as the schrundline. Assuming that the convex transition between steeper and flatter headwall section constitutes the upper limit of enhanced headwall retreat e. g. by periglacial weathering inside the bergschrund, we further address this headwall section as the schrundwall.

 

Geotechnical data (foliation dip and direction) has been digitalised and interpolated in a yet oversimplified manner, to distinguish  headwalls into cataclinal, anaclinal and orthoclinal slopes. Slope inclination and foliation dip has been interrelated to identify e. g. particularly sensitive overdip slopes. First results show that anaclinal and orthoclinal as well as cataclinal headwalls are quite common features in the study area. However, overdip slopes with steeply (30°-60°) outdipping foliation are almost exclusively found in schrundwall sections.

 

The persistence of steep overdip schrundwalls may be related to permafrost occurrence, which is subject to further analysis. Our approach, applied to modeled subglacial topography, may be of great value to anticipate future paraglacial instabilities in glacier headwalls.

How to cite: Ewald, A. and Otto, J.-C.: Paraglacial Cirque Headwall Instability - Regional Scale Assessment Of Preconditioning Factors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17195, https://doi.org/10.5194/egusphere-egu2020-17195, 2020.

EGU2020-5050 | Displays | CR4.1

Pore water pressure dynamics in a rock slope adjacent to a retreating valley glacier

Marc Hugentobler, Simon Loew, and Clément Roques

Rock slope instabilities normally form through long-term strength degradation of initially stable slopes. The rate of progressive damage accumulation in the rock slope is expected to vary over time depending on the current environmental conditions. It is often assumed that glacial retreat, with its increased dynamics in the thermal and hydraulic boundary conditions in combination with mechanical ice unloading induce stresses that cause increased rock mass damage in adjacent slopes. However, direct field measurements to understand these dynamics and to quantify damage are rare.

In this contribution we present new data of a continuous borehole monitoring system installed in a stable rock slope beside the retreating glacier tongue of the Great Aletsch Glacier (Swiss Alps). Special focus lies on the pore water pressure evolution in order to better understand the origin of the presumably hydro-mechanically forced deformation measured in the study area. We compare data of two borehole pressure sensors installed at 50 m depth in the fractured crystalline rock, pressure fluctuations measured in a sink hole on the glacier close to our study site, and glacial melt water discharge measurements. These data show that the pore pressure variability in the slope is driven by annual snowmelt infiltration cycles, rainfall events, and the connection to the englacial water of the temperate valley glacier. We show that our in-situ measurements provide critical data to improve the understanding of the effects of a retreating valley glacier on the boundary conditions and eventually the stability of an adjacent rock slope.

How to cite: Hugentobler, M., Loew, S., and Roques, C.: Pore water pressure dynamics in a rock slope adjacent to a retreating valley glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5050, https://doi.org/10.5194/egusphere-egu2020-5050, 2020.

EGU2020-10159 | Displays | CR4.1

Strategies for the monitoring of rapid changes in paraglacial systems

Lucia Felbauer, Martin Mergili, and Andrea Fischer

Glaciers are retreating at an historically unprecedented pace. Climate-determined processes are changing markedly. As a result, proglacial areas are expanding. Paraglacial dynamics are expected to further increase in significance, controlling sediment supply and landscape change in mid- to high latitudes for the next few hundred years. Paraglacial adjustment in proglacial areas has not been fully explored to date and there is an urgent need to monitor and understand these systems in more detail.

We present first insights into a planned project called glacier2go aiming to investigate changes in the paraglacial system in the highly variable and sensitive areas determined by rapid glacier retreat at two Austrian glaciers. The project aims at the development of a new holistic monitoring system, where remote sensing and field work data are combined and integrated to achieve a deeper understanding of the different stages of evolution of the paraglacial system, and to detect changes through classification approaches. The project glacier2go will fill a research gap by developing an automatic land cover classification model with very high spatial and temporal resolution for monitoring geomorphic changes. glacier2go will capture surface changes through contrasting geomorphic-classification maps.

The proposed survey will be conducted on selected glacier forefields in the Austrian Alps with Jamtalferner (Tyrol, Silvretta) and Pasterze (Carinthia, Glockner range) as the main study sites. glacier2go will be executed as a dissertation project hosted at the Interdisciplinary Institute of Mountain Research (IGF) in Innsbruck, Austria. International cooperation partners in the field of geomorphology, photogrammetry and geoinformation are on board to realize this project.

At the current stage first data comparisons are shown, emphasising the needed research on the interlinkage of geomorphology and the methodical development of new monitoring systems. Setting these first insights into the framework of paraglacial geomorphology leads to the emergence of new research questions. The associated challenges and first approaches for their solution are presented at the conference.

How to cite: Felbauer, L., Mergili, M., and Fischer, A.: Strategies for the monitoring of rapid changes in paraglacial systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10159, https://doi.org/10.5194/egusphere-egu2020-10159, 2020.

EGU2020-21253 | Displays | CR4.1

Bedload dynamics in the rapidly changing paraglacial zone of a high alpine catchment

Clemens Hiller, Kay Helfricht, Gabriele Schwaizer, Severin Hohensinner, Kerstin Wegner, Florian Haas, and Stefan Achleitner

High mountain environments have been confronted with rising temperatures and geomorphological changes over the past 150 years, with the considerable retreat of glaciers constituting one of the most pronounced impacts in the Alps. Concurrent degradation of permafrost in headwalls exposed from the downwasting ice and in periglacial hillslopes alongside glaciers causes increasing sediment flux onto glacier surfaces. The accumulation of supraglacial debris at the current glacier tongue promotes water-storage in debris-covered ice bodies and is assessed as an important source of sediment in the proglacial zone, since a close connection to the fluvial channel network can be assumed. The evolution of mountain streams, the degree of connectivity and conditional sedimentation-erosion effects significantly determine the dynamics in a generally unstable paraglacial landscape in which retreating glaciers provide high stream discharges while sediment is widely unconsolidated.

In the recent scientific debate, the anticipated progressive shift from supply-limitation (fluvial transport overcapacity) to transport-limitation (abundance of sediment) in high alpine catchment areas is discussed. Thus, this study intends to contribute by investigating the connection of coarse sediment including supraglacial debris from the proglacial transition zone to downstream fluvial transport. Key aspect is the feedback between increasing debris cover and a shifting runoff regime due to a changing composition of glacier melt, snow melt and heavy rainfall events. In that respect, the focus will be on the dynamics of bedload transport and the proglacial coarse sediment budget.

This study is part of the Hidden.Ice project and conducts in-depth monitoring of the connectivity, runoff measurements and geomorphological surveys at the LTER site Jamtalferner, Silvretta Range, Austria. Hydraulic modelling of the potential transport capacity supported by bedload trap measurements, the analysis of grain size distribution in the proglacial area and sediment volume changes calculated from UAV-based photogrammetry are aimed at raising knowledge on hydrological and geomorphological dynamics.

How to cite: Hiller, C., Helfricht, K., Schwaizer, G., Hohensinner, S., Wegner, K., Haas, F., and Achleitner, S.: Bedload dynamics in the rapidly changing paraglacial zone of a high alpine catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21253, https://doi.org/10.5194/egusphere-egu2020-21253, 2020.

EGU2020-685 | Displays | CR4.1

Linking glacial lake expansion with glacier dynamics: An assessment of the South Lhonak lake, Sikkim Himalaya

Saurabh Kaushik, Pawan Kumar Joshi, Tejpal Singh, and Anshuman Bhardwaj

The Himalayan Cryosphere is imperative to the people of south and central Asia owing to its water availability, hydropower generation, environmental services, eco-tourism, and influences on overall economic development of the region. Additionally, this influences the energy balance of the earth and contributes significantly to the sea level rise. Therefore Himalayan Cryosphere remains center of attraction for scientific community.  Glacier dynamics, seasonal snow and glacial lakes are studied at various scales using a combination of remote sensing and field observations. The existing literature reveals heterogeneous behavior of Himalayan glaciers which is largely influenced by climate change, debris cover and presence of glacial lake at the terminus. There are very limited studies that attempt to comprehend glacier dynamics and lake expansion in the Eastern Himalayan region. Therefore the present study aims to demonstrate link between glacier dynamics and lake expansion of South Lhonak glacier which is situated in the northern Sikkim. Multitemporal remote sensing data (Landsat, 1979-2019) and climate data (1990-2017) observed at Gangtok meteorological station are used in the study. The results reveal that the lake has expanded with a rate of 0.026 km2 yr-1 during the last four decades. The preliminary results show strongly imbalanced state of glacier, as glacier has deglaciated (area and length), and surface flow velocity and ice thickness have reduced significantly. The statistical analysis (Mann Kendall and Sens slope) of climate data measured at Gangtok meteorological station shows an accelerated trend of mean maximum (0.031°C yr-1) and mean minimum (0.043°C yr-1) temperatures (95% confidence interval). Whereas, no significant trend in total annual precipitation was observed. Inference can be drawn from study that glacier slow down and retreat contribute significantly to the glacial lake expansion under the influence of climate change, such lake expansion pose anticipated risk of glacial lake outburst in the region.

How to cite: Kaushik, S., Joshi, P. K., Singh, T., and Bhardwaj, A.: Linking glacial lake expansion with glacier dynamics: An assessment of the South Lhonak lake, Sikkim Himalaya, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-685, https://doi.org/10.5194/egusphere-egu2020-685, 2020.

EGU2020-19854 | Displays | CR4.1

Ice thickness measurements of the debris covered Ngozumpa glacier, Nepal

Lindsey Nicholson, Fabien Maussion, Christoph Mayer, Hamish Pritchard, Astrid Lambrecht, Anna Wirbel, and Christoph Klug

The presence of extensive debris cover on glaciers in parts of High Mountain Asia increases the certainty about the present day amount of ice, its ongoing rate of change and resultant impact on global sea level rise, regional water and local hazards

Here we use ground penetrating radar measurements of ice thickness for the Ngozumpa glacier, a large debris-covered glacier in Nepal, to explore the challenges of using such data to calculate glacier volume, and to compare how these field measurements compare to the modelled glacier thickness for this glacier generated by the four models used in the global consensus glacier ice thickness dataset, which suggested the region holds 27% less ice than previous estimates (Farinotti and others, 2019). We also compare the ice thickness measured at Ngozumpa glacier to existing data from the smaller neighboring Khumbu glacier and evaluate the maximum volume of a possible moraine dammed lake at this site.

How to cite: Nicholson, L., Maussion, F., Mayer, C., Pritchard, H., Lambrecht, A., Wirbel, A., and Klug, C.: Ice thickness measurements of the debris covered Ngozumpa glacier, Nepal , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19854, https://doi.org/10.5194/egusphere-egu2020-19854, 2020.

EGU2020-20639 | Displays | CR4.1

Results of the IACS Debris-covered Glaciers Working Group melt model intercomparison

Francesca Pellicciotti, Adria Fontrodona-Bach, David Rounce, and Lindsey Nicholson

Many mountain ranges across the globe support abundant debris-covered glaciers, and the proportion of glacierised area covered by debris is expected to increase under continuing negative mass balance. Within the activities of a newly established IACS Working Group (WG) on debris-covered glaciers, we have been carrying out an intercomparison of melt models for debris-covered ice, to identify the level of model complexity required to estimate sub-debris melt. This is a first necessary step to advance understanding of how debris impacts glacier response to climate at the local, regional, and global scale and accurately represent debris-covered glaciers in models of regional runoff and sea-level change projections.

We compare ice melt rates simulated by 15 models of different complexity, forced at the point scale using data from nine automatic weather stations in distinct climatic regimes across the globe. We include energy-balance models with a variety of structural choices and model components as well as a range of simplified approaches. Empirical models are run twice: with values from literature and after recalibration at the sites. We then calculate uncertainty bounds for all simulations by prescribing a range of plausible parameters and varying them in a Monte Carlo framework. We restrict the comparison to the melt season and exclude conditions as few current models have the capability to account for them.

Model results vary across sites considerably, with some sites where most models show a consistently good performance (e.g. in the Alps) which is also similar for energy-balance and empirical models, and sites where models diverge widely and the performance is overall poorer (e.g. in New Zealand and the Caucasus). It is also evident that with a few exceptions, most of the simpler, more empirical models have poor performance without recalibration. A few of the energy-balance models consistently give results different to the others, and we investigate structural differences, the impact of temporal resolution on the calculations (hourly versus daily) and the calculation of turbulent fluxes in particular.    

We provide a final assessment of model performance under different climate forcing, and evaluate models strengths and limitations against independent validation data from the same sites. We also provide suggestions for future model improvements and identify missing model components and crucial knowledge gaps and which require further attention by the debris-covered glacier community.

How to cite: Pellicciotti, F., Fontrodona-Bach, A., Rounce, D., and Nicholson, L.: Results of the IACS Debris-covered Glaciers Working Group melt model intercomparison, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20639, https://doi.org/10.5194/egusphere-egu2020-20639, 2020.

EGU2020-5954 | Displays | CR4.1

The geomorphology of debris-covered Ponkar Glacier, Nepal

Neil Glasser, Adina Racoviteanu, Stephan Harrison, Matthew Peacey, Rakesh Kayastha, and Rijan Bhakta Kayastha

Understanding the evolution of debris-covered glaciers in High Mountain Asia is important for making informed projections of climate change impacts and associated water security and hazard-related issues.  Here we describe the geomorphology of Ponkar Glacier, a debris-covered glacier in Nepal using high-resolution images from 2017 and 2019 based on Unmanned Aerial Vehicle (UAV) flights collected over the glacier and surrounding area in the field. These are used to describe the overall glacier morphology and its ice-surface geomorphology.  The key features of the glacier and its ice-surface morphology are described, including size and extent of tributary glaciers; changes in % of debris cover, lakes, ponds, ice cliffs, crevasses, and vegetation. Geomorphological mapping is used to describe the proglacial geomorphology, outwash plains and proglacial streams, the development of new ice-marginal ponds and changes in vegetation. We use these data to make inferences about the processes of moraine formation in this area. 

How to cite: Glasser, N., Racoviteanu, A., Harrison, S., Peacey, M., Kayastha, R., and Kayastha, R. B.: The geomorphology of debris-covered Ponkar Glacier, Nepal , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5954, https://doi.org/10.5194/egusphere-egu2020-5954, 2020.

EGU2020-22638 | Displays | CR4.1

The debris cover surface of Ponkar glacier: a laboratory for learning

Adina E. Racoviteanu, Neil F. Glasser, Smriti Basnett, Rakesh Kayastha, and Stephan Harrison

Understanding the evolution of debris-covered glaciers, including their evolution over time, the distribution of surface features such as exposed ice walls and supraglacial lakes, and their contributions to glacier ice melt and to glacier-related hazards such as Glacier Lake Outburst Flood (GLOF) events requires an interdisciplinary approach, with a combination of remote sensing methods and collaborative fieldwork.

Since 2017, the IGCP 672 /UNESCO project led has been focussing on the transfer of scientific knowledge on monitoring debris-covered glaciers to local partner institutions in high Asia through trainings, workshops and field collaborations. Our long-term goal is to disseminate methodologies developed under this project to local institutions in high Asia and to embed scientific knowledge into local communities. Here we report on recent capacity building activities held within the context of this new project involved local participants from universities in Nepal and Sikkim. The training included remote sensing/GIS modules, temperature measurements, sediment logging and drone surveys of the ablation zone, which will allow us to better quantify the surface features and their evolution.

 

How to cite: Racoviteanu, A. E., Glasser, N. F., Basnett, S., Kayastha, R., and Harrison, S.: The debris cover surface of Ponkar glacier: a laboratory for learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22638, https://doi.org/10.5194/egusphere-egu2020-22638, 2020.

EGU2020-16328 | Displays | CR4.1

The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing

Anna Wirbel, Lindsey Nicholson, Christoph Mayer, and Astrid Lambrecht

The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing

Debris-covered glaciers are a feature of many mountain ranges around the world and their proportion is expected to increase under continued climate warming.

The impact of debris cover on glacier behavior, via its profound modification of the glacier ablation regime, causes debris-covered glaciers to respond to the same climate forcing in a markedly different way to clean ice glaciers. In order to better understand how debris cover impacts the glacier’s response to climate forcing, we revisit the concept of steady state and examine it for a debris-covered glacier system. We present simple modeling results to explore how the development and evolution of debris cover affects the potential for steady-state and how feedbacks instigated by supraglacial debris cover complicate the glacier’s response to a prescribed steady climate. These investigations highlight the non-stationarity induced by the presence of debris and as a result, that debris cannot be considered as a static component, as it is a highly dynamic component which affects the glacier system in different ways.



How to cite: Wirbel, A., Nicholson, L., Mayer, C., and Lambrecht, A.: The challenge of non-stationary feedbacks within the response of debris-covered glaciers to climate forcing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16328, https://doi.org/10.5194/egusphere-egu2020-16328, 2020.

Debris cover is particularly prevalent in High Mountain Asia, with SW Asia alone containing 3,264 km2 of debris-covered ice (Scherler et al., 2018), which is increasing over time (Thakuri et al., 2014). The presence of supraglacial debris alters the energy balance by either enhancing or inhibiting ablation, depending on its thickness (Östrem, 1959). Therefore, debris cover is fundamental to the response of Himalayan glaciers to climate change. However, there remains a need to understand the glaciological characteristics that control the spatial pattern of debris cover and thus how it may evolve in the future.

Previous research has explored some controls of the spatial distribution of debris cover on a glacier scale (Gibson et al., 2017; Nicholson et al, 2018), but this research will take place on a regional scale. The chosen area is a ~9300 km2 region in the eastern Himalayas that encompasses both Ngozumpa and Lirung glaciers.

The GAMDAM glacier inventory (Sakai et al. 2019) will be used to delineate the glaciers. Within each glacier, the debris extent and thickness will be determined. Extent will be estimated through the supervised classification of optical imagery, using training data obtained from high-resolution Google Earth imagery. Thickness will be calculated through the derivation of a relationship between thermal satellite data (redistributed to a finer spatial resolution) and debris thickness measurements of Lirung glacier (McCarthy et al., 2017) and of Ngozumpa glacier (Nicholson et al., 2018).

An 8m DEM (from NSIDC) will be used to calculate slope, aspect and curvature over each glacier and repeat-pass SAR acquisitions will be used to calculate the velocity field for each glacier. The statistical relationship between debris extent and thickness with each of the aforementioned glacier characteristics is the intended output. Sensitivity tests will subsequently be carried out to determine the relative influence of each glaciological characteristic.

How to cite: Boxall, K. and Willis, I.: Glaciological controls on the spatial variability of supraglacial debris extent and thickness in the eastern Himalayas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20062, https://doi.org/10.5194/egusphere-egu2020-20062, 2020.

EGU2020-6650 | Displays | CR4.1

Spatial distribution of debris cover and its impacts in the Hunza River Basin

Yong Zhang, Shiyin Liu, and Xin Wang

Hunza River is an important tributary of the Indus River, which contributes ~12% of the total runoff in the upper Indus River. 25% of Hunza River basin is covered by glaciers. The Karakoram Highway (KKH) connecting Pakistan and China goes from the Khunjerab Pass and down to the Gilgit, which is an important section of the Pakistan-China Economic Corridor in the high mountains. Many glaciers in this region are extensively covered by supraglacial debris, which strongly influences glacier melting and its spatial pattern. Changes in these glaciers may threaten the stability of the highway subgrade through meltwater floods, unpredictable behaviors of glacier terminals as well as potential outburst floods of glacier lakes near glaciers. Therefore, predicting runoff, response to climate change and risk of outburst floods of debris-covered glaciers requires different treatment to that of clean glaciers in the Hunza River Basin. In this study, we estimate the thermal resistance of the debris layer for the whole basin based on ASTER images. Our results reveal that debris-covered glaciers account for 69% and 30% of the total number and area in the basin. Using a physically-based debris-cover effect assessment model, we find different debris-cover effects on different glaciers, with important implications for the morphology and evolution of glacier hydrological system and associated hazards.

How to cite: Zhang, Y., Liu, S., and Wang, X.: Spatial distribution of debris cover and its impacts in the Hunza River Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6650, https://doi.org/10.5194/egusphere-egu2020-6650, 2020.

EGU2020-11588 | Displays | CR4.1

Carbon gas cycling in supraglacial debris covers

Ben Brock, Grace Brown, Paul Mann, and Stuart Dunning

Debris-covered glaciers extend over 4000 km2 in the high Asian Mountains and are significant and expanding features of most of the World’s glacierized mountain ranges. Within supraglacial debris covers, a combination of fresh mechanically-weathered rock and an abundance of water and energy during melt seasons provides an ideal environment for chemical rock weathering and microbial activity. These processes involve exchange of carbon dioxide CO2 and methane CH4 with the atmosphere, while daytime heating of debris leads to evaporation of meltwater from the debris matrix. Debris-covered glaciers may therefore play an important role in regional and global cycling of major greenhous gases. This new project aims to address 2 key questions: (i) What are the important chemical and microbiological processes affecting carbon gas exchange within supraglacial debris covers? (ii) What are the rates and controls on gas exchange and how do these rates vary in time and space? Initial direct measurements of CO2 flux have been made using an eddy covariance (EC) and gas analyser system installed over debris cover at Miage glacier in the Italian Alps, during the melt season. Under fine weather conditions, there is a strong daily cycle in downwardly-directed CO2 flux, closely linked to variation in energy input to the debris, driven by the flux of shortwave radiation. In contrast, rainfall is associated with short pulses of upwardly-directed CO2 flux to the atmosphere. In common with previously published findings, these data indicate that supraglacial debris covers are a strong summer sink of CO2. At Miage glacier the mean summer (June-August) flux is almost 0.5 g carbon per day per square metre of debris, more than 2 orders of magnitude higher than reported fluxes over cryoconite. Current gas flux data are limited to a few points and this project will extend measurements to varying lithologies, elevations and glaciers in different climatic environments using portable greenhouse gas analysers in conjunction with the EC system. Direct flux measurements will be supported by in-field analysis of debris strucure and composition and subsequent laboratory analysis to determine the minerals, carbon content and microbial communities present in debris covers to uncover controlling processes and determine the relative roles of chemical weathering and microbial activity in carbon gas cycling.

How to cite: Brock, B., Brown, G., Mann, P., and Dunning, S.: Carbon gas cycling in supraglacial debris covers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11588, https://doi.org/10.5194/egusphere-egu2020-11588, 2020.

EGU2020-10825 | Displays | CR4.1

A catastrophic Late Pleistocene debris flow sourced in the glaciated High Atlas of Morocco

Madeleine Hann, Jamie Woodward, Philip Hughes, and Edward Rhodes

Catastrophic events such as debris flows and big floods are important agents of landscape change in steepland mountain environments. These events can be prominent in paraglacial settings as well as those that are tectonically active.   Since such catastrophic events pose  a significant natural hazard in deglaciating modern settings (e.g. Haeberli et al. 2017), it is useful to better understand analogous events in the recent geological past.

The Tamatert Valley, near the village of Imlil, on the northern slopes of Jebel Toubkal (4167 m a.s.l.) in the High Atlas, holds a valuable record of Quaternary landscape change.  The steepland Tamatert Valley was glaciated during the Pleistocene (Hughes et al. 2018)  and lies on the major Tizi n’Test Fault Zone.

More than 200 well rounded basalt mega-boulders (>2m b axis) have been mapped in the Tamatert Valley catchment (9 km2). Many of the boulders are larger than 5 m (b axis). The mega-boulders are found in the active channel of the Tamatert River, stranded above the modern channel, and embedded in valley-fill deposits. A preliminary chronological framework, combining cosmogenic exposure and luminescence dating, points to deposition of these boulders in the Late Pleistocene. The boulders are porphyritic basalt and lithologically distinct from the local diorite/granite bedrock.  They were transported by a catastrophic flood or debris flow over a distance of more than 3 km from the glaciated basalt source area.

Serendipitously, a debris flow producing a similarly extensive deposit of boulders (up to 3 m b axis) occurred in the neighbouring Mizane Valley in September 2019. Mapping of this modern deposit allows direct comparison with the Late Pleistocene event. Together, these provide valuable insights into the geomorphological significance of high magnitude, large boulder transit events in glaciated, steepland river catchments in the High Atlas. 

Haeberli, W., Schaub, Y. & Huggel, C. 2017. Increasing risks related to landslides from degrading permafrost into new lakes in de-glaciating mountain ranges. Geomorphology, 293, 405–417
Hughes, P.D., Fink, D., Rodés, Á., Fenton, C.R. & Fujioka, T. 2018. Timing of Pleistocene glaciations in the High Atlas, Morocco: New10Be and36Cl exposure ages. Quaternary Science Reviews, 180, 193–213

How to cite: Hann, M., Woodward, J., Hughes, P., and Rhodes, E.: A catastrophic Late Pleistocene debris flow sourced in the glaciated High Atlas of Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10825, https://doi.org/10.5194/egusphere-egu2020-10825, 2020.

EGU2020-11290 | Displays | CR4.1

Estimating the style and duration of former glaciation in the mountains of Britain and Ireland

Iestyn Barr, Jeremy Ely, Matteo Spagnolo, Ian Evans, and Matt Tomkins

With a view to better understanding landscape evolution, we model the style and duration of former mountain glaciation in Britain and Ireland during the Quaternary (i.e., the past 2.6 Ma). We use a simple mass balance model, driven by published temperature depression data from the Greenland Ice Core Project (for the past 120 ka), and from a benthic δ18O stack (for the Quaternary as a whole). Though there are limitations to this approach, results provide first-order estimates and indicate that during the Quaternary as a whole, the mountains of Britain and Ireland were glacier-free for 1.1 ± 0.5 Ma; occupied by small (cirque) glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. During the most recent glacial cycle specifically (i.e., the last 120 ka), these areas were glacier-free for an average of 52.0 ± 21.2 ka; occupied by small (cirque) glaciers for 16.2 ± 9.9 ka; and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka. Here, we investigate some of the regional variability in these estimates, and consider implications for long-term landscape evolution.

How to cite: Barr, I., Ely, J., Spagnolo, M., Evans, I., and Tomkins, M.: Estimating the style and duration of former glaciation in the mountains of Britain and Ireland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11290, https://doi.org/10.5194/egusphere-egu2020-11290, 2020.

Pronounced morphologic changes such as coastal retreat and delta progradation occur widely along the Arctic coastal regions in response to increased sediment flux, freshwater runoff, and wave activity caused by climate changes. Compared to open coast and large-scale deltas in the Arctic region, the coastal morphodynamics and associated sediment transport in the Arctic fluvial-tidal transition zone (FTTZ) are less well understood. A series of recurved spits are developed on the upper intertidal zone of microtidal flats in the FTTZ of deglaciated Dicksonfjorden, Svalbard. The morphodynamics and sediment fluxes of the spit complexes were quantified using unmanned aerial vehicle (UAV)-assisted photogrammetry and Real-Time Kinematic GPS. Repeated annual survey indicates that the spits have elongated at 22 m yr-1 and have migrated landward at 4.3 m yr-1 over the last four years. The growth and migration rate of the spits increases seaward, where coastal cliffs consisting of an unconsolidated mixture of angular gravels and muds retreats at 0.2 m yr-1 with net erosion rate of 0.02 m yr-1 and provides local sediment source for the spits. In contrast, isolated gravel ridges, i.e., cheniers, on the tidal flats in the further landward did not migrate during the survey period. Archives of aerial photographs indicate that the cheniers had remained stationary since the 1930s, when a shoreline was located near the cheniers. The present study demonstrates that wave-induced overwash and longshore drift of coarse-grained sediments originated from the retreating cliffs are vital to the annual spit morphodynamics even in the innermost part of the fjord. Tidal flat progradation accelerated since the Little Ice Age with global warming trends by increased runoff from snow-fed rivers and alluvial fans, controls the centennial spit morphodynamics and distribution of wave-built morphology in the FTTZ of glacier-free Dicksonfjorden by regulating episodic sediment delivery via a seaward-shift in the locus of wave shoaling.

How to cite: Kim, D., Jo, J., and Choi, K.: Coastal morphodynamics in an Arctic fluvial-tidal transition zone in the deglaciated Dicksonfjord, Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13381, https://doi.org/10.5194/egusphere-egu2020-13381, 2020.

In the south-western part of Jersika Plain (SE Latvia), the late Pleistocene aeolian sediments form the inland dune field located at Dviete village. This dune field with surface >112 km2 represents the evidence of aeolian activity and landscape evolution during the transition from glacial to post-glacial conditions in this region. The dunes have developed on the surface of glaciolacustrine plain, where subaqueous sedimentation in the Nīcgale ice-dammed lake took place during the retreat of glacier, the Pomeranian phase of the last glaciation.

Here, we focus on reconstructing paleoenvironmental conditions in this region, as inferred from landforms morphology, aeolian sand granulometry and geochemistry, and efficient wind directions derived from DEM. It will contribute to better understanding the processes of landscape evolution conditioned by last deglaciation in SE Latvia.

Results indicate that single parabolic dunes typically have U-shaped configuration in planar view. Aeolian landforms also link and override each other, presenting clustered groups. GIS analysis reveals that the dominating wind directions during the development of dunes would have been westerly to easterly. Previously published dates on OSL chronology for this dune field indicate the initial phase of aeolian activity at around 15.5 Ka and 14.5 Ka. Hence, when the studied landforms formed in presumably paraglacial landscape, the Scandinavian Ice Sheet (SIS) was still present, and most likely atmospheric circulation in this region was affected by anticyclone over the SIS.

The mean grain size Mz of the aeolian deposits forming inland dune field ranges between 143 μm and 256 μm. Hence aeolian landforms are composed mainly of fine-grained sands. It indicates the dominance of saltation and a balance between sand particles and comparatively low energy of local wind power during the aeolian processes. The sediments demonstrate well and moderately well sorting with σ values between 0.473 and 0.707 phi. Granulometry elucidates symmetrical distribution of particles of different fraction with small both negative and positive skewness Sk values ranging from -0.048 to 0.112 phi. For the values of kurtosis KG, results showed that sand is mainly mesokurtic.

Geochemical analysis points out that elemental composition is rather typical for aeolian sediments, determined by the dominance of quartz and K-silicates. Among REE elements, only Y un Nb were identified in detectable concentrations. Similar geochemical signatures across the dune field suggest the provenance of sediments from one main source, possibly associated with glaciofluvial sediment transportation by extra-glacial waters draining from the already ice-free parts of adjoining uplands to the glacial lake.

As apparent from the limited number of paleosoils, aeolian deposition seems to nearly instantly follow the drainage of the Nīcgale ice-dammed lake. It is most likely that cold and dry climate in conjunction with low groundwater tables during the late Pleistocene – beginning of Holocene were among the main controlling factors which prevented development of vegetation cover in this region and delayed stabilisation of the dunes. In turn, it facilitates the action of wind over glaciolacustrine plain as the main driving process of aeolian morphogenesis during the initial evolution of metastable post-glacial landscape.

How to cite: Soms, J. and Egle, Z.: Inland dune field and deposits at Dviete: evidences of the late Pleistocene aeolian morphogenesis and landscape evolution during transition from glacial to post-glacial conditions in South-eastern Latvia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11220, https://doi.org/10.5194/egusphere-egu2020-11220, 2020.

CR4.2 – Permafrost: Open Session (Part 1, Morning, General Contributions; Part 2, Afternoon, Retrogressive Thaw Slumps)

EGU2020-8473 | Displays | CR4.2 | Highlight

Integrating subsea permafrost into an Earth System Model (MPI-ESM)

Stiig Wilkenskjeld, Paul Overduin, Frederieke Miesner, Matteo Puglini, and Victor Brovkin

Subsea permafrost on the Arctic Shelf originates as terrestrial permafrost which was submerged by ocean water following sea level rise during deglaciation. The thickness and depth of subsea permafrost are not well known on the circumpolar scale. Subsea frozen sediments contain organic carbon as well as preventing the upward diffusion of carbon-containing greenhouse gases. Thawing of subsea permafrost – which may accelerate as a consequence of global warming – makes this carbon available for release to the ocean-atmosphere system and thus constitutes a positive feedback to global warming. Present estimates of the carbon associated with subsea permafrost range over two orders of magnitude and are thus highly uncertain and the amount of stored organic carbon potentially huge. Due to the long time scales involved in thawing permafrost, subsea permafrost may become – especially in a future with low anthropogenic carbon emissions – a significant contributor to global carbon releases and thus to an enhanced global warming.

 

The best tool for estimating the effects of future carbon releases are the Earth System Models (ESMs) which, however, are – due to their computational demands – not well suited for the long time scale of build-up and degradation of subsea permafrost. We therefore apply a novel two-model approach. The multiple glacial-cycle model Submarine Permafrost Map (SuPerMap) was used to obtain the pre-industrial distribution of permafrost based on 1D modelling of heat flow driven by glacial, marine and aerial surface upper boundary conditions. This state was then used to initialize JSBACH, the land surface component of the MPI Earth System Model (MPI-ESM), which was extended to allow subsea permafrost applications. JSBACH was used to generate present-day and near-future permafrost thaw by applying historical and future scenario forcings from the MPI-ESM runs performed within the Coupled Model Intercomparison Project, CMIP6. As a first step we here present the modelled physical state (temperature and ice content profiles) of the subsea sediments on the Arctic Shelf in the pre-industrial and present states as well as in the near future. SuPerMap generated a region of cryotic (<0°C) sediment on the Arctic Shelf of 2.5 million km2, more than 80% of which lay north of Eastern Siberia. In the JSBACH simulations, permafrost thawing rates accelerate after the mid-20th century. From about 2060 onwards, the choice of shared social-economic pathway (SSP) determines the rate of thaw and up to about 1/3 of the pre-industrial cryotic area is lost before year 2100. Regional aspects of the SSP projections will be presented.

How to cite: Wilkenskjeld, S., Overduin, P., Miesner, F., Puglini, M., and Brovkin, V.: Integrating subsea permafrost into an Earth System Model (MPI-ESM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8473, https://doi.org/10.5194/egusphere-egu2020-8473, 2020.

The ground surface over permafrost area subsides and uplifts annually due to the seasonal thawing and freezing of active layer. GPS Interferometric Reflectometry (GPS-IR) has been successfully applied to the signal-to-noise ratio (SNR) observations to retrieve elevation changes of frozen ground surface at Barrow, Alaska. In this study, the method is extended to include GLONASS and Galileo SNR observations. Based on the multiple SNR observations collected by SG27 in Barrow, the multiple GNSS-IR time series of ground surface elevation changes during snow-free days from late June to middle October in year 2018 are obtained at daily intervals. All the three time series show a similar pattern that the ground subsided in thaw season followed by uplifts in freezing season, which is well characterized by the previous composite physical model using thermal indexes. Fitted with the composite model, the amplitude of the GPS-derived elevation changes during the snow-free days is suggested to be 3.3 ± 0.2 cm. However, the time series of GLONASS-IR and Galileo-IR measurements are much noisier than that of GPS-IR due to their inconsistent daily satellite tracks. Applied with a specific strategy in the composite model fitting, the amplitudes of GLONASS- and Galileo-derived elevation changes are estimated to be 4.0 ± 0.3 cm and 3.9 ± 0.5 cm, respectively. Then, GLONASS-IR and Galileo-IR time series are reconstructed in turn with the fitting coefficients. Moreover, the occurrences of the short-term variations in time series of GNSS-IR measurements are found to coincidence with the precipitation events, indicating the hydrologic control on the movements of frozen ground surface. The results presented in this study show the feasibility to combine multiple GNSS to densely monitor frozen ground surface deformations, and provide an insight to understand the impacts of both thermal and hydrologic forces on the frozen ground dynamics.

How to cite: Hu, Y.: Ground surface elevation changes estimated using multiple GNSS signal-to-noise ratio observations over permafrost area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6841, https://doi.org/10.5194/egusphere-egu2020-6841, 2020.

EGU2020-10903 | Displays | CR4.2 | Highlight

20 years of mountain permafrost monitoring in the Swiss Alps: key results and major challenges

Jeannette Noetzli and Cécile Pellet

Permafrost is a widespread thermal subsurface phenomenon in polar and high mountain regions and was defined as an essential climatic variable (ECV) by the Global Climate Observing System (GCOS). The Swiss Permafrost Monitoring Network was started in the year 2000 as an unconsolidated network of sites from research projectsand as the first national long-term observation network for permafrost it is an early component of the Global Terrestrial Network for Permafrost (GTN-P). After 20 years of operation, development and evaluation, PERMOS holds the largest and most diverse collection of mountain permafrost data worldwide and has a role model regarding its structure and organization. PERMOS aims at the systematic long-term documentation of the state and changes of mountain permafrost in the Swiss Alps. The scientific monitoring strategy is now based on three observation elements: ground-surface and subsurface temperatures, changes in subsurface ice content, and permafrost creep velocities. These three elements complement each other in a landform-based approach to capture the influence of the topography as well as the surface and subsurface conditions of different landforms on the ground thermal regime. These influences are considered to be more relevant than regional climatic conditions in the small country.

Over the past 20 years, all observation elements indicate a clear warming trend of mountain permafrost in the Swiss Alps. Borehole temperatures generally increase at 10 and 20 m depth. This warming trend was intensified after 2009 and temporarily interrupted following winters with a thin and late snow cover, particularly winter 2016. Further, the trend is more pronounced at cold permafrost sites like rock glacier Murtèl-Corvatsch, where an increase of +0.5°C has been observed at 20 m over the past 30 years. For permafrost temperatures close to 0 °C, climate warming does not result in significant temperature increase but is masked by phase changes and latent heat effects. These result in significant changes in ice content, which can be registered by electrical resistivity tomography (ERT). Further, the warming trend of mountain permafrost in the Swiss Alps is corroborated by increasing creep rates of rock glaciers, which follow an exponential relationship with ground temperatures. In this contribution, we present and discuss the key results from two decades of mountain permafrost monitoring within the PERMOS network. In addition to the measurement data, we identified considerable challenges for long-term monitoring network of mountain permafrost based on experience collected over two decades. The acquisition of reliable data at a limited number of stations in extreme environments with difficult access requires robust strategies, standards and traceability for the entire data acquisition chain: installation > measurement > raw data > processing > archiving and, finally, reporting.

How to cite: Noetzli, J. and Pellet, C.: 20 years of mountain permafrost monitoring in the Swiss Alps: key results and major challenges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10903, https://doi.org/10.5194/egusphere-egu2020-10903, 2020.

EGU2020-10183 | Displays | CR4.2

Measuring and modelling thermal erosion patterns of peat plateaus in northern Norway

Sebastian Westermann, Leo Martin, Jan Nitzbon, Kjetil Aas, Johanna Scheer, Trond Eiken, and Bernd Etzelmüller

Peat plateaus are a major type of permafrost landscape in Arctic and Siberian lowlands. They represent a substantial pool of several hundreds of petagrams of organic carbon that has the potential to contribute to the Permafrost Carbon Feedback. The thermal response of these soils to the climate signal is complex and implies the interaction of various surface and subsurface processes operating at a very small spatial scale involving water, snow and heat fluxes and surface subsidence. As these processes have the ability to generate feedbacks between each other and trigger non-linear evolutions of the landscape, they challenge our abilities to measure and model them.

Peat plateaus in Northern Norway have been actively degrading over at least the last 60 years. They thus offer a precious opportunity to measure and model the degradation patterns they exhibit. We present new topographical observations derived from drone-based photogrammetry that we acquired for one site in Northern Norway. Over a period of 3 years, these Digital Elevation Models allows quantifying precisely the surface subsidence and resulting lateral degradation of the peat plateaus. In a second time, we use the land surface model CryoGrid to model the observed patterns. The model is able to (i) simulate the snow fluxes and the water and heat sub-surface fluxes within the plateau and between the plateau and the surrounding wet mire and to (ii) represent the soil surface subsidence due to excess ice melt in the soil. We implement a set up that discretize the interface between the peat plateaus and the wet mire and force the Surface Energy Balance module of the model with climatic data derived from regional atmospheric modelling.

Our simulations manage to reproduce the degradation speed we observe in our topographical data. We also present a sensitivity analysis of the degradation speed to snow cover and to the geometry of the peat plateaus and show how the feedbacks between the dynamical topography and the lateral fluxes of snow and water can trigger rapid permafrost thawing and fast degradation of permafrost landscapes.

How to cite: Westermann, S., Martin, L., Nitzbon, J., Aas, K., Scheer, J., Eiken, T., and Etzelmüller, B.: Measuring and modelling thermal erosion patterns of peat plateaus in northern Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10183, https://doi.org/10.5194/egusphere-egu2020-10183, 2020.

EGU2020-21805 | Displays | CR4.2

Decade of permafrost thaw in a subarctic palsa mire alters carbon fluxes without affecting net carbon balance

Carolina Olid, Jonatan Klaminder, Sylvain Monteux, Margareta Johansson, and Ellen Dorrepaal

Snow depth increases observed in some artic regions and its insulations effects have led to a winter-warming of permafrost-containing peatlands. Permafrost thaw and the temperature-dependent decomposition of previously frozen carbon (C) is currently considered as one of the most important feedbacks between the artic and the global climate system. However, the magnitude of this feedback remains uncertain because winter effects are rarely integrated and predicted from mechanisms active in both surface (young) and thawing deep (old) peat layers.

Laboratory incubation studies of permafrost soils, in situ carbon flux measurements in ecosystem-scale permafrost thaw experiments, or measurements made across naturally degrading permafrost gradients have been used to improve our knowledge about the net effects of winter-warming in permafrost C storage. The results from these studies, however, are biased by imprecision in long-term (decadal to millennial) effects due to the short time scale of the experiments. Gradient studies may show longer-term responses but suffer from uncertainties because measurements are usually taken during the summer, thus ignoring the long cold season. The need for robust estimates of the long-term effect of permafrost thaw on the net C balance, which integrates year-round C fluxes sets the basis of this study.

Here, we quantified the effects of long-term in situ permafrost thaw in the net C balance of a permafrost-containing peatland subjected to a 10-years snow manipulation experiment. In short, we used a peat age modelling approach to quantify the effect of winter-warming on net ecosystem production as well as on the underlying changes in surface C inputs and losses along the whole peat continuum. Contrary to our hypothesis, winter-warming did not affect the net ecosystem production regardless of the increased old C losses. This minimum overall effect is due to the strong reduction on the young C losses from the upper active layer associated to the new water saturated conditions and the decline in bryophytes. Our findings highlight the need to incorporate long-term year-round responses in C fluxes when estimating the net effect of winter-warming on permafrost C storage. We also demonstrate that thaw-induced changes in moisture conditions and plant communities are key factors to predicting future climate change feedbacks between the artic soil C pool and the global climate system.

How to cite: Olid, C., Klaminder, J., Monteux, S., Johansson, M., and Dorrepaal, E.: Decade of permafrost thaw in a subarctic palsa mire alters carbon fluxes without affecting net carbon balance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21805, https://doi.org/10.5194/egusphere-egu2020-21805, 2020.

EGU2020-16115 | Displays | CR4.2

Climate extremes relevant for permafrost degradation

Goran Georgievski, Stefan Hagemann, Dmitry Sein, Dmitry Drozdov, Andrew Gravis, Vladimir Romanovsky, Dmitry Nicolsky, Alexandru Onaca, Florina Ardelean, Marinela Chețan, and Andrei Dornik

During the past several decades, Arctic regions warmed almost twice as much as the global average temperature. Simultaneously in the high northern latitudes, observations indicate a decline in permafrost extend and landscape modifications due to permafrost degradation. Climate projections suggest an accelerated soil warming, and consequently deepening of the active layer thickness in the near future. Except air temperature, two other parameters i.e. precipitation and snow depth are the most important climatic parameters affecting the thermal state and extend of the permafrost. The key research question of this study is whether or not certain climatic conditions can be identified that can be considered as an extreme event relevant for permafrost degradation. Here we apply data mining techniques on meteorological re-analysis to develop a coherent framework for the identification of extreme climate conditions relevant for active soil layer deepening and a decline of permafrost extend.
Several key types of events have been classified based on various combinations of temperature, precipitation and snow depth statistics. Then, the respective events have been identified in ERA-Interim reanalysis and evaluated against in situ observations in West Siberia region. The evaluation proved that the developed algorithm could successfully detect relevant extreme climate conditions in meteorological re-analysis dataset. It also indicated possibilities to improve the algorithm by refining definitions of extreme events. Refinement of algorithm is currently work in progress as well as the evaluation against satellite observations and a hierarchy of numerical models. Nevertheless, the method is applicable for all kinds of gridded climatological datasets that contain air temperature, precipitation and snow depth.

Acknowledgement
This work is funded in the frame of ERA-Net plus Russia. TSU is supported by MOSC RF # 14.587.21.0048 (RFMEFI58718X0048), AWI and HZG are supported by BMBF (Grant no. 01DJ18016A and 01DJ18016B), and WUT by a grant of the Romanian National Authority for Scientific Research and Innovation, CCDI-UEFISCDI, project number ERANET-RUS-PLUS-SODEEP, within PNCD III

How to cite: Georgievski, G., Hagemann, S., Sein, D., Drozdov, D., Gravis, A., Romanovsky, V., Nicolsky, D., Onaca, A., Ardelean, F., Chețan, M., and Dornik, A.: Climate extremes relevant for permafrost degradation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16115, https://doi.org/10.5194/egusphere-egu2020-16115, 2020.

Ground surface subsidence caused by the melt of excess ice is a key geomorphic process in permafrost regions. Subsidence can damage infrastructure, alter ecology and hydrology, and influence carbon cycling. The Geological Survey of Canada maintains a network of thaw tubes in northwestern Canada, which records annual thaw penetration, active-layer thickness, and ground surface elevation changes at numerous sites. Measurements from the early 1990s from 17 sites in the Mackenzie Delta area have highlighted persistent increases in thaw penetration in response to rising air temperatures. These increases in thaw penetration have been accompanied by significant ground surface subsidence (~5 to 20 cm) at 10 ice rich sites, with a median subsidence rate of 0.4 cm a-1 (min: 0.2, max: 0.8 cm a-1). Here we present preliminary results comparing these long-term field data to simulations for two observation sites using the Northern Ecosystem Soil Temperature (NEST) model. NEST has been modified to include a routine that accounts for ground surface subsidence caused by the melt of excess ground ice. The excess ice content of upper permafrost in the simulations was estimated based on ratios between thaw penetration and subsidence measured at each thaw tube. The NEST simulations begin in 1901, and there is little ground surface subsidence until the 1980s. The simulated rate of ground surface subsidence increases in the 1990s. The modelled ground surface subsidence is in good agreement with the measured annual magnitudes and longer-term patterns over the measurement period from 1992 to 2017. This preliminary assessment indicates that the modified NEST model is capable of predicting gradual thaw subsidence in ice-rich permafrost environments over decadal timescales.

How to cite: O'Neill, H. B. and Zhang, Y.: Simulation and validation of long-term ground surface subsidence in continuous permafrost, western Arctic Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20012, https://doi.org/10.5194/egusphere-egu2020-20012, 2020.

EGU2020-12498 | Displays | CR4.2 | Highlight

Slope thermokarst transforms permafrost preserved glacial landscapes and effects propagate through Arctic drainage networks.

Steve Kokelj, Justin Kokoszka, Jurjen van der Sluijs, Ashley Rudy, Jon Tunnicliffe, Sarah Shakil, Suzanne Tank, and Scott Zolkos

Recent intensification of slope thermokarst is transforming permafrost preserved glaciated landscapes and causing significant downstream effects. In this paper we: A) Describe the thaw-related mechanisms driving the evolution of slope to stream connectivity; B) define the watershed patterns of thermokarst intensification; and C) project the cascade of effects through the Arctic drainage networks of northwestern Canada. The power-law relationships between disturbance area and volume, and thickness of permafrost thawed, in conjunction with a time-series of disturbance mapping show that the non-linear intensification of slope thermokarst is mobilizing vast stores of previously frozen glacial sediments linking slopes to downstream systems. Mapping across a range of catchment scales indicates that slope thermokarst predominantly affects first and second order streams. Slope sediment delivery now frequently exceeds fluvial transport capacity of these streams by several orders of magnitude indicating long-term perturbation. Mapping shows slope thermokarst is directly affecting over 6760 km of stream segments, over 890 km of coastline and over 1370 lakes across the 1,000,000 km2 Arctic drainage basin from continuous permafrost of northwestern Canada. The downstream projection of thermokarst disturbance increases affected lakes by a factor of 4 and stream length by a factor of 7, and suggests that fluvial transfer has the potential to yield numerous thermokarst impact zones across coastal areas of western Arctic Canada. The Prince of Wales Strait between Banks and Victoria Islands is identified as a hotspot of downstream thermokarst effects, and the Peel and Mackenzie rivers stand out as principle conveyors of slope thermokarst effects to North America’s largest Delta and to the Beaufort Sea. The distribution of slope thermokarst and the fluvial pattern of sediment mobilization signal the climate-driven rejuvenation of post-glacial landscape change and the triggering of a time-transient cascade of downstream effects. Geological legacy and the patterns of continental drainage dictate that terrestrial, freshwater and marine environments of western Arctic Canada will be a hotspot of climate-driven change through the coming centuries. 

How to cite: Kokelj, S., Kokoszka, J., van der Sluijs, J., Rudy, A., Tunnicliffe, J., Shakil, S., Tank, S., and Zolkos, S.: Slope thermokarst transforms permafrost preserved glacial landscapes and effects propagate through Arctic drainage networks. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12498, https://doi.org/10.5194/egusphere-egu2020-12498, 2020.

EGU2020-6965 | Displays | CR4.2

Monitoring rapid permafrost thaw using elevation models generated from satellite radar interferometry

Philipp Bernhard, Simon Zwieback, Silvan Leinss, and Irena Hajnsek

Vast areas of the Arctic host ice-rich permafrost, which is becoming increasingly vulnerable to terrain-altering thermokarst in a warming climate. Among the most rapid and dramatic changes are retrogressive thaw slumps. These slumps evolve by a retreat of the slump headwall during the summer months, making them detectable by comparing digital elevation models over time using the volumetric change as an indicator. Despite the availability of many topographic InSAR observations to generate digital elevation models, there is currently no method to map and analyze retrogressive thaw slumps. 
Here, we present and assess a method to detect and monitor thaw slumps using time-series of elevation models (DEMs), generated from single-pass InSAR observations, which have been acquired across the Arctic at high resolution since 2011 by the TanDEM-X satellite pair.  At least three observations over this timespan are available with a spatial resolution of about 12 meter and the height sensitivity of 0.5-2 meter. We first difference the generated digital elevation and detect significant elevation changes taking the uncertainty estimates of each elevation measurement into account. In the implementation of the processing chain we focused on making it as automated as much as possible to be able to cover large areas of the northern hemisphere. This includes detecting common problems with the data and apply appropriate algorithms to obtain DEMs with high accuracy. Additionally we implemented methods to deal with problematic features like wet-snow, vegetation and water bodies. After generating the DEMs we us DEM differencing followed by a blob detection and cluster algorithm to detect active thaw slumps. To improve the accuracy of our method we apply and compare different machine learning methods, namely a simple threshold method, a Random Forest and a Support-Vector-Machine. To estimate the accuracy of our method we use data from past studies as well as a classification based on optical satellite data.
The obtained locations of thaw slumps can be used as a starting point to extract important slump properties, like the headwall height and volumetric change, which are currently not available on regional scales. Additionally to the thaw slump detection, we show first results of the thaw slump property extraction for thaw slumps located in Northern Canada (Peel Plateau, Mackenzie River Delta, Banks Island, Ellesmere Island). 

How to cite: Bernhard, P., Zwieback, S., Leinss, S., and Hajnsek, I.: Monitoring rapid permafrost thaw using elevation models generated from satellite radar interferometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6965, https://doi.org/10.5194/egusphere-egu2020-6965, 2020.

EGU2020-14201 | Displays | CR4.2

Multi-methodological investigation of a retrogressive thaw slump in the Richardson Mountains, Northwest Territories, Canada

Julius Kunz, Christof Kneisel, Tobias Ullmann, and Roland Baumhauer

The Mackenzie-Delta Region is known for strong morphological activity in context of global warming and permafrost degradation, which reveals in a large number of retrogressive thaw slumps. These are frequently found along the shorelines of inland lakes and the coast; however, this geomorphological phenomenon also occurs at inland ​​streams and creeks of the Peel Plateau and the Richardson Mountains, located in the southwest of the delta. Here several active retrogressive thaw slumps are found of which some have reached an extent of several hectares, e.g. the mega slump at the Dempster Creek.

In this study we investigated a recent retrogressive thaw slump at the edge of the Richardson Mountains close to the Dempster Highway to determine the subsurface properties using non-invasive geophysical methods. We performed three-dimensional Ground Penetrating Radar (GPR) surveys, as well as quasi-three-dimensional Electrical Resistivity Tomography (ERT) surveys in order to investigate the subsurface characteristics adjacent to the retreating headwall of the slump. These measurements provide information on the topography of the permafrost table, ice content and/or water pathways on top, within or under the permafrost layer. Additionally, we performed manual measurements of the active layer thickness for validation of the geophysical models. The approach was complemented by the analysis of high-resolution photogrammetric digital elevation models (DEM) that were generated using in situ drone acquisitions.

The measured active layer depths show a strong influence of the relief and especially of small creeks on the permafrost table topography. Likely, this influence also is the primary trigger for the initial slump activity. In addition, the ERT measurements show strong variations of the electrical resistivity values in the upper few meters, which are indicative for heterogeneities, also within the ice-rich permafrost body. Especially noticeable is a layer of low resistivity values in an area adjacent to the slump headwall. This layer is found at depths between 4m to 7m, which approximately corresponds to the base of the headwall. Here, the low resistivity values could be indicative for an unfrozen or water-rich layer below the ice-rich permafrost. Consequently, this layer may have contributed to the initial formation of the slump and is important for the spatial extension of the slump.

These results present new insights into the subsurface of an area adjacent to an active retrogressive thaw slump and may contribute to a better understanding of slump development.

How to cite: Kunz, J., Kneisel, C., Ullmann, T., and Baumhauer, R.: Multi-methodological investigation of a retrogressive thaw slump in the Richardson Mountains, Northwest Territories, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14201, https://doi.org/10.5194/egusphere-egu2020-14201, 2020.

EGU2020-7176 | Displays | CR4.2

Characterization of mobilized sediments and organic matter in retrogressive thaw slumps on the Peel Plateau, NWT, Canada

Lisa Bröder, Kirsi Keskitalo, Scott Zolkos, Sarah Shakil, Suzanne Tank, Tommaso Tesi, Bart van Dongen, Negar Haghipour, Timothy Eglinton, and Jorien Vonk

The Peel Plateau in northwestern Canada hosts some of the fastest growing “mega slumps”, retrogressive thaw slumps exceeding 2000 m2 in area. The region is located at the former margin of the Laurentide ice sheet and its landscape is dominated by ice-rich hummocky moraines. Rapid permafrost thaw resulting from enhanced warming and increases in summer precipitation has been identified as a major driver of sediment mobilization in the area, with some of the largest slumps relocating up to 106 m3 of previously frozen sediments into fluvial networks. The biogeochemical transformation of this thawed substrate within fluvial networks may represent a source of CO2 to the atmosphere and have a large impact on downstream ecosystems, yet its fate is currently unclear. Concentrations of dissolved organic matter are lowered in slump-impacted streams, while the particle loads increase. Here, we aim to characterize the mobilized material and its sources by analyzing active layer, Holocene and Pleistocene permafrost, debris (recently thawed, still at the headwall) and slump outflow samples from four different slumps on the Peel Plateau. We use sediment properties (mineral surface area, grain size distribution), carbon isotopes (13C, 14C) and molecular markers (solvent-extractable lipids, lignin phenols, cutin acids, non-extractable compound classes analyzed by pyrolysis-GCMS) in order to assess the composition and quality of the mobilized sediment and organic matter and thereby improve our understanding of their fate and downstream effects. Preliminary results show that organic matter content and radiocarbon age in debris and outflow from all four slumps are dominantly derived from Holocene and Pleistocene permafrost soils with a smaller influence of the organic-rich active layer. Degradation proxies based on extractable lipid and lignin biomarkers suggest Holocene and Pleistocene permafrost organic matter to be more matured than the fresh plant material found in the active layer, while debris and outflow samples show a mixed signal. For the non-extractable organic matter, aromatics and phenols make up the largest fraction of all samples. Lignin markers are almost exclusively found in the active layer samples, which also contain a larger proportion of polysaccharides, while N-containing compounds and alkanes make up the remaining 2-25 % with no obvious patterns. Active layer soils also have the highest median grain sizes, whereas Pleistocene permafrost soils consist of much finer mineral grains. Samples collected at the slump outflow are significantly more homogeneous (i.e., showing a narrower grain size distribution) than any of the other samples. We thus infer that both organic matter degradation and hydrodynamic sorting during transport play a role within these slump features; determining their relative magnitudes will be crucial to better assess potential feedbacks of these increasingly abundant “mega slumps” to changing climate.

How to cite: Bröder, L., Keskitalo, K., Zolkos, S., Shakil, S., Tank, S., Tesi, T., van Dongen, B., Haghipour, N., Eglinton, T., and Vonk, J.: Characterization of mobilized sediments and organic matter in retrogressive thaw slumps on the Peel Plateau, NWT, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7176, https://doi.org/10.5194/egusphere-egu2020-7176, 2020.

EGU2020-10567 | Displays | CR4.2

Downstream persistence of particulate organic carbon released from thaw slumps on the Peel Plateau, NT, Canada

Sarah Shakil, Suzanne Tank, Steve Kokelj, and Jorien Vonk

Underlain by ice-rich permafrost, the Peel Plateau in western Canada is highly susceptible to rapid permafrost degradation in the form of retrogressive thaw slumps and has experienced a non-linear intensification in the area, volume, and thickness of permafrost thawed since 2002. These slumps tend to occur along stream networks, which flow directly into the Peel River, through the Mackenzie Delta, and into the Beaufort Sea. Thus, lateral transport of previously sequestered organic carbon from these features has the potential to propagate far downstream. Upstream-downstream comparisons have shown that thaw slumps mobilize material to stream systems primarily in the form of particulate organic carbon (POC), increasing organic carbon yields by orders of magnitude, and switching stream networks to particle-dominated systems. Furthermore, the bulk POC released from slumps can be upwards of 10,000 14C years old, and base-extracted fluorescence measurements suggest material is more reworked since terrestrial production compared to upstream material.

To determine how far this effect propagates downstream we measured particulate and dissolved organic carbon (DOC) fluxes across stream transects extending 0.4 to 1 km downstream of thaw slumps in 1st to 2nd order streams and found no consistent decrease in TSS or POC fluxes with transit downstream.  In addition, we measured the composition (%POC, C:N, fluorescence, D14C) and flux of DOC and POC within the ~1100 km2 Stony Creek watershed, examining tributary streams representing different vegetative, slump-density, and geological units in addition to the Stony Creek mainstem, to determine contributions to downstream flux. We found organic carbon fluxes were dominated by slump-mobilized POC at all points downstream of disturbance, and that these organic carbon fluxes were greater than any non-disturbed tributary stream. The 14C age of POC along the Stony Creek mainstem increased by thousands of years with the introduction of slump inputs and remained similarly depleted in 14C at the watershed outlet. Using historical suspended sediment, POC, and discharge data for the 75,000 km2 Peel River drainage basin containing the Stony Creek watershed, we will examine whether there have been increases in instantaneous sediment and POC fluxes during the thaw season to track the trends of intensifying slump activity that have been documented on the Peel Plateau. Constraining the downstream effect of these abrupt, localized disturbances may improve detection and prediction of change that will likely cascade through the region over the coming decades.

How to cite: Shakil, S., Tank, S., Kokelj, S., and Vonk, J.: Downstream persistence of particulate organic carbon released from thaw slumps on the Peel Plateau, NT, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10567, https://doi.org/10.5194/egusphere-egu2020-10567, 2020.

Around the Arctic Ocean there are many stretches of coastline composed of ice-rich sediments. With the dramatic climatic, oceanic and terrestrial changes that are currently occurring, there is considerable concern over the stability of these coasts and how they are being altered. With the complexity that permafrost conditions add to the coastal setting, modelling erosion involves a more detailed understanding of the physical and thermal conditions as well as the sedimentological and wave action processes. This research examines the role that the shallow water energy balance plays in preserving sub-bottom massive ice as the coastline retreats and the implications it has for secondary subsea disturbance once the water depth increases.

The study area was Peninsula Point which is approximately 10 km west of Tuktoyaktuk, NWT, Canada. The massive ice and retrogressive thaw slumps at this location are some of the more dramatic examples of the impact of ice-rich permafrost on coastal processes in the Arctic. By mapping the area with satellite and aerial imagery and conducting repeat ground penetrating radar surveys (GPR) over a 30 year period, the long-term character of coastal retreat above, and below, the water line is revealed. In winter, the GPR was pulled behind a snowmobile along transects on land, across the shoreline and out onto the near shore area of the Beaufort Sea. This provided the stratigraphic continuity between the terrestrial and sub-sea settings. The GPR revealed the massive ice and sedimentary architecture, from which vertical and lateral relationships to the coastline were determined. The roles of erosion, re-sedimentation and shallow-water thermodynamics in the degradation and preservation of massive ground ice were revealed. Using this new information, modeling of the coastal retreat and sediment contributions to the ocean demonstrated a much more complex system than previously assumed.

How to cite: Moorman, B.: Submarine preservation of massive tabular ground ice by coastal retrogressive thaw slumps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11343, https://doi.org/10.5194/egusphere-egu2020-11343, 2020.

EGU2020-8806 | Displays | CR4.2

Retrogressive thaw slumps along permafrost coasts transform organic matter before release into the Arctic Ocean

George Tanski, Hugues Lantuit, Dirk Wagner, Christian Knoblauch, Saskia Ruttor, Boris Radosavljevic, Juliane Wolter, Michael Fritz, Jens Strauss, Anna M. Irrgang, Justine Ramage, Torsten Sachs, and Jorien E. Vonk

Changing environmental conditions in the Arctic have profound impacts on permafrost coasts, which erode at great pace. Although numbers exist on annual carbon and sediment fluxes from coastal erosion, little is known on how terrestrial organic matter (OM) is transformed by thermokarst and –erosional processes on transit from land to sea. Here, we investigated a retrogressive thaw slump (RTS) on Qikiqtaruk - Herschel Island in the western Canadian Arctic. The RTS was classified into an undisturbed, disturbed and nearshore zone and systematically sampled along transects. Collected sediments were analyzed for organic carbon (OC), nitrogen (N), stable carbon isotopes (δ13C-OC) and ammonium. C/N-ratios, δ13C-signatures and ammonium concentrations were used as general indicator for OM degradation. Permafrost sediments from the RTS headwall and mud lobe sediments from the thaw stream outlet were incubated to further assess OM degradation and potential greenhouse gas formation during slumping and upon release into the nearshore zone. Our results show that OM concentrations significantly decrease upon slumping in the disturbed zone with OC and N decreasing by >70% and >50%, respectively. Whereas δ13C-signatures remain fairly stable, C/N-ratios decrease significantly and ammonium concentrations increase slightly in fresh slumping material. Nearshore sediments have low OM contents and a terrestrial signature comparable to disturbed sites on land. The incubations show that carbon dioxide (CO2) forms quickly from thawing permafrost deposits and mud debris with ~2-3 mg CO2 per gram dry weight being cumulatively produced within two months. We suggest that the initial strong decrease in OM concentration after slumping is caused by a combination of OC degradation, dilution with melted massive ice and immediate offshore transport via the thaw stream. After stabilization in the slump floor, recolonizing vegetation takes up N from the disturbed sediment. Upon release into the nearshore zone, larger portions of OM are directly deposited in marine sediments, where they further degrade or being buried. The incubations indicate that CO2 is rapidly produced upon slumping and potentially continues to form within the nearshore zone that receives eroded material. We conclude that coastal RTS systems profoundly change the characteristic of modern and ancient permafrost terrestrial OM during transit from land to sea - a process which is likely linked to the production of greenhouse gases. Our study provides valuable information on the potential fate of terrestrial OM along eroding permafrost coasts under the trajectory of a warming Arctic.

How to cite: Tanski, G., Lantuit, H., Wagner, D., Knoblauch, C., Ruttor, S., Radosavljevic, B., Wolter, J., Fritz, M., Strauss, J., Irrgang, A. M., Ramage, J., Sachs, T., and Vonk, J. E.: Retrogressive thaw slumps along permafrost coasts transform organic matter before release into the Arctic Ocean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8806, https://doi.org/10.5194/egusphere-egu2020-8806, 2020.

EGU2020-12142 | Displays | CR4.2

Using ArcticDEM to identify and quantify pan-Arctic retrogressive thaw slump activity

Chunli Dai, Melissa Jones, Ian Howat, Anna Liljedahl, Antoni Lewkowicz, and Jeffrey Freymueller

With the increased availability and coverage of high resolution satellite imagery, characterizing processes at the pan-Arctic scale is now possible. This baseline pan-Arctic product will enable us to highlight areas for future research efforts and to standardize observations that are currently locally or regionally focused. The ArcticDEM project (www.arcticdem.org) has released a large collection of 2 meter resolution Digital Elevation Models (DEMs) for all land areas above 60 °N. These DEMs are created using high resolution (~0.5 m) stereo paired satellite images (by DigitalGlobe and include Worldview- 1 (launched 2007), 2 (2009), 3 (2014) and GeoEye-1 (2008) satellites). Using repeat DEMs, we are developing algorithms for automated detection to identify and quantify land surface topographic changes from Arctic volcano eruptions and mass wasting events to create a pan-Arctic mass wasting inventory, including retrogressive thaw slumps. Currently, retreat rates reported for retrogressive thaw slumping activity differ between studies, and our dataset will enable rates to be standardized for slump activity after 2007. Furthermore, our mass wasting inventory will enable us to investigate the triggers of mass wasting events and to analyze the linkages to the contributing factors including climate, topography, and geology. We will be presenting preliminary results focusing specifically on retrogressive thaw slumps, including time series analysis for topographic change detection and using field observations for validation. We welcome collaborators who can share the field or remote sensing observations to aid in our validation efforts.

How to cite: Dai, C., Jones, M., Howat, I., Liljedahl, A., Lewkowicz, A., and Freymueller, J.: Using ArcticDEM to identify and quantify pan-Arctic retrogressive thaw slump activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12142, https://doi.org/10.5194/egusphere-egu2020-12142, 2020.

EGU2020-360 | Displays | CR4.2

Daily monitoring of retrogressive thaw slumps in the Fosheim Peninsula, Ellesmere Island, Canada

Melissa Ward Jones, Benjamin Jones, and Wayne Pollard

Retrogressive thaw slumps (RTS) occur from the mass wasting of ice-rich permafrost. These horseshoe-shaped features have an ablating or retreating ice-rich headwall with fluidized sediment that is transported along the RTS floor. RTS can remain active for up to decades and enlarge as the headwall retreats. With observed increases in RTS number, rates and sizes in recent decades, there is a need to understand these highly dynamic landforms, however there is a general lack of detailed field observations of RTSs. We monitored 3 RTS for over half of the 2017 thaw period by setting up and tracking survey transects on a near daily basis. We correlated mean daily and cumulative retreat to mean daily air temperature (MDAT), total daily precipitation (TDP) and thawing degree days (TDD) using various polynomial regressions and Pearson correlation techniques. Our results show that July retreat was highly variable and periods of increased RTS retreat did not always align with periods of increased air temperature. Also, multiple periods of increased retreat could occur within a single period of increased air temperature. These retreat trends were observed to be largely driven by sediment redistribution in the RTS floor. Retreat rates decreased suddenly in early August, indicating a threshold of either air temperature, solar radiation or a combination of both must be reached for increased retreat rates. There was a statistically significant correlation between daily mean and mean cumulative retreat with MDAT (p < 0.001) and TDD (p < 0.001 and < 0.0001) but not with TDP. Correlating mean cumulative retreat and cumulative TDD using polynomial regression (quadratic and cubic) generated R2 values greater than 0.99 for all 3 sites as these variables account for past and current conditions within the monitoring period, as well as lag responses of retreat. This suggests the potential of accurately modelling RTS retreat with minimal field data (air temperature and headwall position), however this is currently restricted to individual RTSs and only within short time scales. We tested this idea by modelling 2 weeks of cumulative retreat in 2018 for 2 of our sites we monitored using the 2017 regression equations. Percent prediction error was 8% at one site and 16% at the other. Monitoring RTS on a daily scale allows RTS behaviour and trends to be identified that may be obscured at annual time scales. With the widespread increased numbers of RTSs being observed around the Arctic, understanding their dynamics is critical as these landforms impact surrounding ecosystems and infrastructure which will be exacerbated with climate change.  

How to cite: Ward Jones, M., Jones, B., and Pollard, W.: Daily monitoring of retrogressive thaw slumps in the Fosheim Peninsula, Ellesmere Island, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-360, https://doi.org/10.5194/egusphere-egu2020-360, 2020.

EGU2020-746 | Displays | CR4.2

The specificity of thermal denudation feature distribution on Yamal and Gydan peninsulas, Russia

Nina Nesterova, Artem Khomutov, Arina Kalyukina, and Marina Leibman

Thermal denudation is a combination of the processes responsible for the formation of retrogressive thaw slumps (cryogenic earth flows) and thermocirques. Thermocirques are the depressions with a semi-circle shape resulting from tabular ground ice thaw. Environments characteristic of Сentral parts of Yamal and Gydan peninsulas forming the so called  Kara sub-latitudinal transect, are favorable to activation of thermal denudation. The key factors are continuous permafrost distribution and shallow occurrence of tabular ground ice.

An increase in ground temperature and active layer thickness in 2012-2013 cause the intensification of thermal denudation along Kara sub-latitudinal transect. Field studies in the area of “Vaskiny Dachi” research station as well as remote sensing of 2018 data demonstrates the presence of both active and stabilized thermocirques during.

This research presents preliminary results of collecting and analyzing the distribution of more than 400 landforms caused by thermal denudation identified in central Yamal and central Gydan peninsulas. Coastal thermodenudation landforms were not taken into account to exclude the influence of wave erosion in this study. Such work became possible due to free of charge satellite images with a very high spatial resolution available at the service Yandex.Maps (https://yandex.ru/maps/).

In Yamal peninsula, we identified 63 active and 53 stabilized thermodenudation landforms, in Gydan peninsula, 169 active and 166 stabilized, respectively. Active thermodenudation features concentrate in the western and southern parts of central Yamal, while stabilized dominate in western and central parts. In central Gydan both active and stabilized features of thermal denudation are located at northwestern part and are distributed more evenly compared to Yamal. Northern border of all identified thermodenudation features for both Yamal and Gydan peninsulas is located at 71 degrees North, and the southern border at 69 degrees North. Despite the difficulties of visual interpretation of thermal denudation features, we defined the majority of them as thermocirques, most of which are located along lake coastlines. Such indication was also confirmed by in-situ data collected during multiyear field campaigns in the study area. These results reveal a prevalence of thermal denudation features in the study area and the collected data gives us an opportunity for spatial analysis of their distribution.

The reported study was partially funded by RFBR according to the research project #18-05-60222 

How to cite: Nesterova, N., Khomutov, A., Kalyukina, A., and Leibman, M.: The specificity of thermal denudation feature distribution on Yamal and Gydan peninsulas, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-746, https://doi.org/10.5194/egusphere-egu2020-746, 2020.

EGU2020-7611 | Displays | CR4.2

Retrogressive thaw slumps in areas with tabular ground ice on Kolguev (Barents Sea) and Novaya Sibir’ (East-Siberian Sea) Islands

Alexander Kizyakov, Frank Günther, Mikhail Zimin, Anton Sonyushkin, Ekaterina Zhdanova, Sebastian Wetterich, and Andrey Medvedev

The activation of retrogressive thaw slumps is associated with slope surface stability disturbances, or with an increase in the depth of seasonal thawing, that can reach the top of surface-near ground ice. Most retrogressive thaw slumps are confined to terraced slope surfaces that have been undercut and started to retreat due to lateral river erosion or wave action along lake, river or sea shores. Subsequent long-term retrogressive that slump growth depends on constant removal of material from the slope foot by river water or sea waves.

We have studied the current dynamics of coastal destruction and retrogressive thaw slumps in the western (Kolguev Island) and one of the eastern-most (Novaya Sibir’ Island) occurrences of tabular ground ice in the Eurasian Arctic. A wide set of multi-temporal optical earth observation data of high and very-high spatial resolution (SPOT 6 & 7, GeoEye, WorldView, Kompsat, Prism, Formosat, and Resurs) was used. We modified the TanDEM-X DEM (12 m) for relief reconstruction of earlier stage relief settings to ensure consistent orthorectification of oblique viewing satellite imagery. All raw images were terrain-corrected and georeferenced using a comprehensive block adjustment.

In the western part of Kolguev Island retrogressive thaw slump average retreat rates of different thermocirque features varied from 0.7 to 7.9 m/year in 2002-2018. Maximum rates reached 14.5-15.1 m/year. On the Novaya Sibir’ Island thermocirques averaged retreat rates in 2007-2018 varied from 3.3 to 8.5 m/year, maximum rates were up to 15.5 m/year.

Besides dependence of thermocirque occurrence on local ground ice conditions, external forcing on coastal dynamics and thermocirque retreat has been analysed for air temperature and sea ice fluctuations through sums of positive daily mean air temperature and the duration of the open-water period variability for specific periods bracketed by image acquisition dates. Ice conditions in the coastal zone (app. near 50 km of coastal line) of the studied areas were analyzed according to microwave satellite OSI-450 and OSI-430 datasets. We assumed the open-water season as the period when sea ice concentration was less than 15%. Around Kolguev Island, over the 2006-2018 there has been not statistically significant linear trend for open-water period - median value of linear trend is 2.5 days/year with different sea ice conditions off the south and north coasts of the island. At the same time, an increase in the annual sum of positive daily mean  air temperature is noted. For the period 2006-2018, the linear trend was 23.2 degree/year. That is why, for Kolguev Island, we expect at least a sustained level of substantially stronger retreat rates when compared with the past, if not a further increase in thermal denudation intensity and thermocirque growth, and strong and steady rates of coastal destruction due to wave action. Further research will focus on identifying commonalities and differences between the two study regions with respect to hydrometeorological and permafrost conditions.

Supported by RFBR grants № 18-05-60080 and 18-05-60221, and by DFG grant № WE4390/7-1.

How to cite: Kizyakov, A., Günther, F., Zimin, M., Sonyushkin, A., Zhdanova, E., Wetterich, S., and Medvedev, A.: Retrogressive thaw slumps in areas with tabular ground ice on Kolguev (Barents Sea) and Novaya Sibir’ (East-Siberian Sea) Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7611, https://doi.org/10.5194/egusphere-egu2020-7611, 2020.

EGU2020-10477 | Displays | CR4.2

Representing Arctic coastal erosion in the Max Planck Institute Earth System Model (MPI-ESM)

David Marcolino Nielsen, Johanna Baehr, Victor Brovkin, and Mikhail Dobrynin

The Arctic has warmed twice as fast as the globe and sea-ice extent has decreased, causing permafrost to thaw and the duration of the open-water period to extend. This combined effect increases the vulnerability of the Arctic coast to erosion, which in turn releases substantial amounts of carbon to both the ocean and the atmosphere, potentially contributing to further warming due to a positive climate-carbon cycle feedback. Therefore, Arctic coastal erosion is an important process of the global carbon cycle.

Comprehensive modelling studies exploring Arctic coastal erosion within the Earth system are still in their infancy. Here, we describe the development of a semi-empirical Arctic coastal erosion model and its coupling with the Max Planck Institute Earth System Model (MPI-ESM). We also present preliminary results for historical and future climate projections of coastal erosion rates in the Arctic. The coupling consists on the exchange of a combination of driving forcings from the atmosphere and the ocean, such as surface air temperature, winds and sea-ice concentration, which result in annual coastal erosion rates. In a further setp, organic matter from the eroded permafrost is provided to the ocean biogeochemistry model and, consequently, to the global carbon cycle including atmospheric CO2.

How to cite: Nielsen, D. M., Baehr, J., Brovkin, V., and Dobrynin, M.: Representing Arctic coastal erosion in the Max Planck Institute Earth System Model (MPI-ESM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10477, https://doi.org/10.5194/egusphere-egu2020-10477, 2020.

EGU2020-17801 | Displays | CR4.2

Thermal behaviour of retrogressive thaw slumps over time revealed by ERT - an example from Herschel Island, Canada

Saskia Eppinger, Michael Krautblatter, Hugues Lantuit, and Michael Fritz

In the last century the number of retrogressive thaw slumps has doubled in some arctic regions, e.g. Herschel Island, Yukon Territory, Canada [Lantuit and Pollard, 2008]. Retrogressive thaw slumps are a common thermocarst landform along the coast of Herschel Island [Lantuit and Pollard, 2005]. However mechanical conditions leading to the evolution of those retrogressive thaw slumps are poorly understood.

For a better understanding of internal thermal processes in these retrogressive thaw slumps we implemented different electrical resistivity profiles (ERT). They cross the focused thaw slump longitudinally and transversally. We compared about 2 km of new ERT-data from 2019 with the same transects from 2011 to gain information about the temperature distribution and the temperature changes in the slump ground.

The aim for our study is to gain a profound understanding of the strong and deep thermal disturbances generated by retrogressive thaw slumps and how they change over time, leading to a possible polycyclicality of these slumps.

 

 

 

 

Lantuit, H., and W. H. Pollard (2005), Temporal stereophotogrammetric analysis of retrogressive thaw slumps on Herschel Island, Yukon Territory, Nat. Hazards Earth Syst. Sci. 5 (3), 413–423.

Lantuit, H., and W. H. Pollard (2008), Fifty years of coastal erosion and retrogressive thaw slump activity on Herschel Island, southern Beaufort Sea, Yukon Territory, Canada, Geomorphology 95 (1-2), 84–102.

How to cite: Eppinger, S., Krautblatter, M., Lantuit, H., and Fritz, M.: Thermal behaviour of retrogressive thaw slumps over time revealed by ERT - an example from Herschel Island, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17801, https://doi.org/10.5194/egusphere-egu2020-17801, 2020.

EGU2020-12181 | Displays | CR4.2

Long-term warming of Holocene winter temperatures in the Canadian Arctic recorded in stable water isotope ratios of ice wedges

Trevor Porter, Kira Holland, Duane Froese, and Steven Kokelj

Rapid and sustained warming of the northern high latitudes has led to increased permafrost thaw and retrogressive thaw slump (RTS) activity in some areas of the Arctic. Thaw slumps are common in the Tuktoyaktuk Coastlands (Northwest Territories, Canada) and expose relict ice wedge polygon networks that contain a long-term record of winter precipitation isotopes. Notably, the stable isotope geochemistry of ice wedges can be used as a paleotemperature proxy for the winter season, a seasonality that is largely missing from current understandings of Holocene paleoclimate change in the Arctic.

 

In this study, we sampled lateral cross-sections of four relict ice wedges from RTS exposures at coastal sites on Hooper Island, Pelly Island, Richards Island and near Tuktoyaktuk. Ice blocks capturing the entire growth sequences of the ice wedges (i.e., ice wedge center to ice-sediment contact) were collected by chainsaw and kept frozen in field coolers, and later sub-sampled at high-resolution in a cold lab. The ice wedges were sub-sampled at 1-1.5 cm horizontal resolution, integrating ~1-3 ice veins per sample on average. We analysed the stable hydrogen- and oxygen-isotope ratios (δ2H and δ18O) of each sample (N = 803). The age of the ice was estimated by AMS-DO14C dating of 6 to 10 samples per ice wedge, evenly distributed across each wedge to capture the full range of ages. A composite δ18O record spanning the period 7,400-600 cal yr BP was also constructed using the dated samples only (N = 36). The all-sample co-isotope (δ2H-δ18O) data are defined by regression line that is remarkably similar to the Local Meteoric Water Line, suggesting the ice wedges reliably preserve the isotopic composition of local precipitation, which is strongly influenced by mean air temperatures. The composite record shows an increase in δ18O over the last 7,400 years which we interpret as a long-term warming trend of the mean winter climate. This warming trend is largely explained by increasing November-April insolation at 69°N, a result that is corroborated by two independent high-resolution ice wedge records from the Siberian Arctic and is also in agreement with model-based simulations of the winter climate. This record, the first of its kind in the North American Arctic, provides a more seasonally holistic perspective on Holocene climate change and highlights the potential to use permafrost isotope records to fill paleoclimate knowledge gaps in Arctic regions were more traditional precipitation isotope archives (e.g., ice cores) do not exist.

How to cite: Porter, T., Holland, K., Froese, D., and Kokelj, S.: Long-term warming of Holocene winter temperatures in the Canadian Arctic recorded in stable water isotope ratios of ice wedges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12181, https://doi.org/10.5194/egusphere-egu2020-12181, 2020.

EGU2020-2999 | Displays | CR4.2

Multi-method dating of ancient permafrost of the Batagay megaslump, East Siberia

Sebastian Wetterich, Julian B. Murton, Phillip Toms, Jamie Wood, Alexander Blinov, Thomas Opel, Margret C. Fuchs, Silke Merchel, Georg Rugel, Andreas Gärtner, and Grigoriy Savvinov

Dating of ancient permafrost is essential for understanding permafrost stability and interpreting past climate and environmental conditions over Pleistocene timescales but faces substantial challenges to geochronology.

Here, we date permafrost from the world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E). The slump headwall exposes four generations of ice and sand-ice (composite) wedges that formed synchronously with permafrost aggradation. The stratigraphy differentiates into a Lower Ice Complex (IC) overlain by a Lower Sand Unit, an Upper IC and an Upper Sand Unit. Two woody beds below and above the Lower Sand Unit represent the remains of two episodes of taiga forest development prior to the Holocene forest. Thus, the ancient permafrost at Batagay potentially provides one of the longest terrestrial records of Pleistocene environments in western Beringia.

We apply four dating methods to the permafrost deposits to disentangle the chronology of the Batagay permafrost archive – optically-stimulated luminescence (OSL) dating of quartz and post-infrared-stimulated luminescence (pIR-IRSL) dating of feldspar as well as accelerator mass spectrometry-based Cl-36/Cl dating of wedge ice and radiocarbon dating of organic material.

The age information obtained so far indicates that the Batagay permafrost sequence is discontinuous and that the Lower IC developed well before MIS 7, the overlying Lower Sand Unit formed during MIS 6, and the Upper IC and the Upper Sand Unit formed both during MIS 3-2.

Additional sampling for all dating approaches presented here took place in spring 2019, and is part of ongoing research to enhance the geochronology of the exceptional palaeoenvironmental archive of the Batagay megaslump.

How to cite: Wetterich, S., Murton, J. B., Toms, P., Wood, J., Blinov, A., Opel, T., Fuchs, M. C., Merchel, S., Rugel, G., Gärtner, A., and Savvinov, G.: Multi-method dating of ancient permafrost of the Batagay megaslump, East Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2999, https://doi.org/10.5194/egusphere-egu2020-2999, 2020.

EGU2020-3748 | Displays | CR4.2

Ground-ice stable-isotope paleoclimatology at the Batagay megaslump, East Siberia

Thomas Opel, Sebastian Wetterich, Hanno Meyer, and Julian Murton

In recent years, permafrost ground ice (i.e. ice wedges and pore ice) has been frequently utilized as a paleoclimate archive for the Late Pleistocene and Holocene, mainly using stable isotopes from water as proxies for local air temperatures. Due to their formation processes (frost cracking in winter and crack infilling mainly with snowmelt in spring), ice wedges have a unique winter seasonality, whereas pore ice integrates summer or annual precipitation.

The world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E), provides unique access to Late and Middle Pleistocene permafrost formations usually deeply buried in the frozen ground. The Batagay megaslump exposes syngenetic ice wedges and composite wedges (ice–sand wedges) along with pore ice in four cryostratigraphic units: (1) the Lower Ice Complex, (2) the Lower Sand, (3) the Upper Ice Complex, and (4) the Upper Sand.

Here, we present ground-ice stable-isotope data from all four units. This dataset is accompanied by precipitation stable-isotope values from winter snowpack and summer rain as a first stable-isotope framework for this region.

The high continentality of the study region with – extremely low winter temperatures – is clearly reflected by the stable-isotope composition for ice wedges from the Upper Ice Complex (MIS 3) and nearby Holocene ice wedges. Both are much more depleted than for any other ice-wedge study site in East Siberia. The ice wedges from the Lower Ice Complex are likely the oldest ice wedges (>0.5 Ma) ever analyzed isotopically and also point to very cold winter climate during formation. Stable-isotope signatures of composite wedges and pore ice are less distinctive and require detailed studies of formation processes and seasonality.

How to cite: Opel, T., Wetterich, S., Meyer, H., and Murton, J.: Ground-ice stable-isotope paleoclimatology at the Batagay megaslump, East Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3748, https://doi.org/10.5194/egusphere-egu2020-3748, 2020.

EGU2020-21041 | Displays | CR4.2

Characterisation of East Siberian paleodiversity based on ancient DNA analyses of the Batagay megaslump exposure

Jeremy Courtin, Amedea Perfumo, Kathleen Stoof-Leichsenring, and Ulrike Herzschuh

With the ongoing Arctic warming, permafrost thaw accelerated during the last decade as much as it is now a global concern for biodiversity loss, food webs and biogeochemical cycling. This rapid permafrost degradation forms features such as massive retrogressive thaw slumps that give access to exceptional records for Quaternary biodiversity change investigations. The Batagay megaslump located in northern Yakutia, East Siberia, is the world’s largest thawslump known to date, and along its ~55m high headwall it gives access to Late and Mid Pleistocene permafrost deposits up to more than 500 kyrs in age. During an expedition to this unique site in 2017, sediment samples were collected with ages from more than 500 kyrs to modern time for the analysis of ancient DNA (aDNA). Our aim is to characterise the biodiversity and changes over geological timescales of this region in East Siberia. Using the aDNA extracted from these ancient environmental samples, we first performed a metabarcoding analysis (chloroplast trnL) to investigate past vegetation composition. We then performed a shotgun metagenomic analysis, which enabled a much higher depth of sequence data and allowed us to access the entire biodiversity, from Eukaryotes to Prokaryotes, Archaea and Viruses. This approach opened up new horizons, making it possible not only to investigate biodiversity composition and changes but also to infer on potential interactions across taxa and kingdoms. Both methods together allowed comparison and ensured robustness of the results obtained. We present here one of the very first studies done on the global, past and modern, biodiversity of permafrost regions which holds an enormous potential to reveal new insights into the evolution of this fragile ecosystem.

How to cite: Courtin, J., Perfumo, A., Stoof-Leichsenring, K., and Herzschuh, U.: Characterisation of East Siberian paleodiversity based on ancient DNA analyses of the Batagay megaslump exposure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21041, https://doi.org/10.5194/egusphere-egu2020-21041, 2020.

The Batagay mega slump is the largest active thaw slump on the planet. Enormously rapid thermal erosion gave access to permafrost sediments that deposited since the Middle Pleistocene. Permafrost is an excellent medium for the preservation of ancient organic matter. The Batagay exposure is well known for some spectacular findings of Pleistocene megaherbivore carcasses including the youngest steppe bison found in Eurasia so far, dated to 8.2 ka BP. The extraordinarily long sequence of Pleistocene deposits in Batagay is therefore an excellent archive of the palaeoenvironmental history in the Yana highlands - a region with uniquely stable cold-continental climate known as the pole of cold in the northern hemisphere. This region is regarded as refugial area for extrazonal steppe plants and now extinct large grazers together constituting the Pleistocene mammoth steppe, which covered vast areas in high and mid latitudes of the northern hemisphere during cold stages. Modern vegetation around the study site consists of light taiga mainly composed of larch, shrub alder, shrub birches and stone pine. To understand the processes that resulted in the demise of Pleistocene megafauna and in the biological turnover during the late Quaternary, we reconstructed vegetation and environmental conditions during the two climate extremes of the late Pleistocene, the onset of the last glacial maximum and the last interglacial using remains of plants and insects preserved in organic-rich material. The results from studies of plant material gathered in a fossil ground squirrel nest suggest that grassland vegetation corresponding to modern meadow steppes in Central Yakutia and northern Mongolia existed in the study area during the last cold stage. During the last interglacial, open coniferous woodland similar to modern larch taiga was the primary vegetation at the site. Abundant charcoal indicates wildfire events during the last interglacial. Zoogenic disturbances of the local vegetation were indicated by the presence of ruderal plants, especially by the abundant nitrophytic Urtica dioica, suggesting that the area was an interglacial refugium for large herbivores. Meadow steppes, which formed the primary vegetation during cold stages and provided potentially suitable pastures for herbivores, were a significant constituent of the plant cover in the Yana Highlands also under the full warm stage conditions of the last interglacial. Consequently, meadow steppes occurred in the Yana Highlands during the entire investigated timespan of the Pleistocene documenting a remarkable environmental stability. The documented fossil record also proves that modern steppe occurrences in the Yana Highlands did not establish as late as in the Holocene, as suggested by some scholars, but instead are relicts of a formerly continuous steppe belt extending from Central Siberia to Northeast Yakutia during the Pleistocene.

How to cite: Kienast, F., Ashastina, K., Kuzmina, S., and Rudaya, N.: Vegetation at the northern pole of cold during the climate extremes of the late Pleistocene: fossil records from the Batagay mega thaw slump, Yakutia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20513, https://doi.org/10.5194/egusphere-egu2020-20513, 2020.

Cryogenic processes, especially “warm” significantly affect the reliability of the northern infrastructure. Thermoerosion is the process of destruction of the banks or ground massives constructed by the permafrost and ground ice, by thermal and mechanical influence of the running water. Tazovskiy peninsula, where the largest gas production facilities are located, is referred in Russia as “The kingdom of the thermoerosion”.

The geodetical level of the surface on Tazovskiy peninsula varies between 15–20 m. and 60–80 m., but the thermoerosion processes are very active. The area exposed to thermoerosion was 10–15% of the territory in the beginning of 1980th and actively enlarges.

The period of the maximum active layer thaw depth is August, when the precipitation amount is the highest, which coupled with the raising trend of the air temperature (0.8°C per decade) (IPCC, 2014) and growing temperature (up to 1.5-2o warmer) of the upper permafrost layers, results in the ground destruction. The appearance of the thermoerosion process we clarify by the highly blurred sediments at the surface: the upper Quaternary silty iced (up to 40–60%) sands or sandy loams. The other auspicious factor is polygonal ice systems formed by iced peatlands (2–3 m of depth) serving as the positions of the future thermoerosion cuts. Our investigations showed that in the raising probability of the erosion occurrence, weak root systems of the shrubs and grasses can not cope with the process.

The factor that significantly intensify the speed of the thermoerosion is active snow melting in May–beginning of June. Together with increasing snowiness of the winters it additionally activies the processes of gullies formation. The conducted field works during the snowmelt revealed lumpy collapsing of the big ground blocks near the lateral sides of the watercourses which was the main reason of erosion speed boost. The blocks remained frozen, the rate of the lateral erosion was 15–20 cm/per day, the widths was up to  1.5–2 m.

We started to observe dynamics of the thermoerosion in early 2000’s. The rate of the gullies growing on the right side of the r. Nyudya-Adlyurdyepoka was up to 10 m. per year. The length of the gully was 60 m. in 2006 and it was U-shaped. In 2016 the gully had length of 80 m.. The profile of the gully became V-shape everywhere, the gully was branched out and the steepness of the edges increased. More detailed characteristics of the other representative gullies development will be consider in this research.

Our study showed that construction and exploitation of the road systems between the deposit fields entailed the formation of linear overmoistured zones near the roads and formed new thermoerosion systems.  

 Satellite data showed that territory occupied by thermoerosion processes raised by 15–20 % in the last 40 years. It is due to climatic changes, the active exploitation of the technogenic systems on iced and easily blurred soils.

This work is supported by the RFBR project â„–18-05-60080 «Dangerous nival-glacial and cryogenic processes and their impact on infrastructure in the Arctic»

How to cite: Tolmanov, V.: Thermoerosion process on Tazovskiy peninsula. Factors and dynamics., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-825, https://doi.org/10.5194/egusphere-egu2020-825, 2020.

Between 2016 and 2018, Gagnon and Allard (2019) investigated the impact of climate change on winter ice-wedge (IW) cracking frequency and IW morphology. In this study, they revisited 16 sites in the Narsajuaq valley (Canada) that were extensively studied between 1989 and 1991. Climate warming only started around 1993 whence mean annual air temperatures started to rise from -10 °C then to about -6 °C nowadays. This gave the unique opportunity to observe and measure changes by directly comparing field data with data pre-dating a climate warming of known amplitude. They found that based on IW tops, the active layer reached depths that were 1.2 to 3.4 times deeper than in 1991, which led to the widespread degradation of IW in the valley. Whereas 94% of the IWs unearthed in 1991 showed multiple recent growth structures, only 13% of the IWs unearthed in 2017 still had such features.

However, about half of the IWs in 2017 had ice veins connecting them to the base of the active layer, an indication that the recent cooling trend (2010-now) in the region was enough to reactivate frost cracking and IW growth. This shows that the soil system can respond quickly to short-term climate variations. For this study, we aimed to determine how changes in surface temperatures affected active-layer thickness (ALT) and dynamics over the past 25 years in order to understand the timing and reaching times of ground temperature thresholds for soil cracking and IW degradation. We used TONE, a one-dimensional finite-element thermal model, to simulate ground temperatures over the past 25 years. A monthly mean air temperature from a reanalysis (1948-2016) was combined with data from a weather station about 9 km west of the study area (2002-2018) to simulate the soil temperature profiles of four typical soil types found in the valley: thick sandy peat cover, thick peat cover, thin sandy peat cover, and fluvial sands.

Our results show that ALT variations were predominantly controlled by changes in thawing season air temperature with regards to the previous year. As soon as 1998, the active layer had already reached the main stages of the IWs, i.e. the largest and oldest part composing the IWs, but it is only from 2006 that the main stages started melt until 2010, an exceptionally warm year. Based on soil temperature thresholds, our results show that IWs remained active until around 2006. This means that as the active layer deepened and caused IW tops degradation, freezing season temperatures were still cold enough to induce soil cracking and IW growth in width. After 2010, the cooling trend was enough to reactivate the IWs from as a soon as 2011. This study shows that prior to advanced degradation, IWs can melt substantively and remain active at the same time as long as freezing season temperatures are cold enough to induce soil contraction cracking. However, it is likely that pulse events such as ground collapse will cause positive feedbacks contributing to rapid IW degradation before the soil completely stops cracking.

How to cite: Gagnon, S. and Allard, M.: Modelled (1990-2100) Variations in Active-Layer Thickness and Ice-Wedge Activity Near Salluit, Nunavik (Canada) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1428, https://doi.org/10.5194/egusphere-egu2020-1428, 2020.

EGU2020-2416 | Displays | CR4.2 | Highlight

The influence of radiative forcing on permafrost temperatures in Arctic rock walls

Juditha Schmidt, Sebastian Westermann, Bernd Etzelmüller, and Florence Magnin

Climate change has a strong impact on periglacial regions and intensifies the degradation of mountain permafrost. This can result in instabilities of steep rock walls as rock- and ice-mechanical properties are modified. Besides altitude and the related air temperature, latitude is a crucial factor, as solar radiation has a strong impact on the energy transfer processes from the atmosphere to the ground. It can differ significantly in intensity and time over latitudinal positions and exposures of frozen rock slopes.

In this project, we suggest improving the parametrization of short-wave and long-wave radiation in thermal models for permafrost degradation. To achieve this, we will analyze temperature data of surface temperature loggers from Southern Norway to Svalbard. In total, 37 loggers were installed between 2010 and 2017. The field sites display enormous latitudinal gradients as well as topographic settings. Furthermore, they provide hourly data, allowing us to set up short-stepped time series for examination of solar radiation angles at varying latitudes.

The data is used to set up a transient heat-flow model (CryoGrid) to simulate the local thermal regime. The model takes into account varying input of short-wave radiation due to aspect, slope angle and time as well as long-wave radiation under different sky-view factors. Finally, the influence of solar radiation on permafrost degradation in steep rock walls is investigated.

How to cite: Schmidt, J., Westermann, S., Etzelmüller, B., and Magnin, F.: The influence of radiative forcing on permafrost temperatures in Arctic rock walls, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2416, https://doi.org/10.5194/egusphere-egu2020-2416, 2020.

EGU2020-2927 | Displays | CR4.2

Slope hydrology and permafrost: The effect of snowmelt N transport on downslope ecosystem

Laura Helene Rasmussen, Per Ambus, Wenxin Zhang, Per Erik Jansson, Anders Michelsen, and Bo Elberling

In the permafrost-affected landscape, surface and near-surface water movement links areas of higher elevation with lowlands and surface water bodies. Water supply is dominated by snow melt and is thus highly seasonal, as most water moves on the frozen surface in spring, passing only a thin layer of thawed soil. Soluble nutrients mobilized by soil thaw may thus be transported laterally from upslope to downslope ecosystems, which in nutrient-limited cold ecosystems may affect vegetation, ecosystem respiration and surface-atmosphere interaction. In a nitrogen (N) limited ecosystem, however, released inorganic N may in reality not travel far downslope.
This study quantifies the potential effect of the snowmelt water nutrient transport by tracing dissolved N in meltwater moving downslope on the frozen surface in a W Greenlandic slope with a snow fan supplying meltwater throughout most of the summer. We use the stable isotopes 15N and D applied simultaneously on top of the frozen surface upslope in a combined solution to investigate the behavior of water and dissolved N flow patterns. We further address the effect of season by tracing N supplied in the early thaw season (30 cm to the frozen surface) and in the late thaw season (90 cm to the frozen surface). Monitoring the slope in detail, we then use the numerical coupled heat-and-mass transfer Coup model to simulate the biotics and abiotics of the receiving ecosystem and study the importance of the lateral N input and the effect of increased N transport in a warmer future.  
About 50 % of the N tracer was retained in the ecosystem immediately below injection in the early growing season (30 cm active layer), whereas about 35 % was retained in the later growing season (90 cm active layer). Most of the applied 15N was rapidly immobilized by microbes and into the bulk soil, whereas only a few percentages was taken up by the vegetation. D recovery seemed to follow the pattern of microbial N uptake, suggesting that N and D moved physically from the frozen surface and to the immediate subsoil together.

Modelling the ecosystem based on measured N and C pool sizes, meteorology, soil temperature and –moisture revealed a large N constrain on vegetation growth. The current observed vegetation could not be explained with the measured pools alone, suggesting an “invisible” source of N to support the observed vegetation. We conclude that a substantial fraction of lateral N input is transported further downslope, but that increases in N release and transport might not affect vegetation immediately, as most supplied N ends in the soil pool. Vegetation in the receiving ecosystem relies on an external N source, which could be dissolved N transported by snowmelt water on the frozen surface. Snowmelt redistribution of N in the landscape may thus be a factor to account for when studying N cycling in a spatial context.

How to cite: Rasmussen, L. H., Ambus, P., Zhang, W., Jansson, P. E., Michelsen, A., and Elberling, B.: Slope hydrology and permafrost: The effect of snowmelt N transport on downslope ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2927, https://doi.org/10.5194/egusphere-egu2020-2927, 2020.

Recent field and modelling studies indicate that a fully-coupled, multi-dimensional, thermo-hydraulic (TH) approach is required to accurately model the evolution of permafrost-impacted landscapes and groundwater systems. However, the relatively new and complex numerical codes being developed for coupled non-linear freeze-thaw systems require validation. This issue was first addressed within the InterFrost IPA Action Group, by means of an intercomparison of thirteen numerical codes for two-dimensional TH test cases (TH2 & TH3). The main results (cf. Grenier et al. 2018 and wiki.lsce.ipsl.fr/interfrost) demonstrate that these codes provide robust results for the test cases considered.

The second phase of the InterFrost project is devoted to the simulation of a cold-room reference experiment based on test case TH2 (Frozen Inclusion). In a first implementation phase of the experimental setup, the initial frozen inclusion was inserted in the setup prior to the complete filling of the porous medium and the flow initiation. The thermal evolution of the system was monitored by thermistors located at the center of the initial inclusion and along the downgradient centerline. This setup provided optimal conditions to control the initial experiment geometries but resulted in slight differences in the initialization time for different experiments.

In a second implementation strategy, we now consider “in place” generation of an initial frozen inclusion through a cooling coil. The initial frozen inclusion is obtained after the initial cooling time and its initial thermal state is measured by means of an array of thermistors. In a second step, the flow is initiated, and the thermal evolution is monitored through an array of 11 thermistors (within the initial position and downgradient).

The experimental setup and an overview of all monitoring results as well as preliminary numerical simulations are presented. In an attempt to prevent formerly observed drifts in total water flowrates, the porous medium is renewed for each single experiment considering some key experimental conditions (full-flow vs. no-flow). A repetition of experiments provides an estimation of experimental uncertainty bounds. Derived results and conclusions from this experiment will form the basis for the next phase within the InterFrost validation exercise.

How to cite: Grenier, C. and Costard, F.: InterFrost Project Phase 2: Updated experiment results for the validation of Cryohydrogeological codes (Frozen Inclusion), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4865, https://doi.org/10.5194/egusphere-egu2020-4865, 2020.

EGU2020-7489 | Displays | CR4.2

Quantification of ground ice through petrophysical joint inversion of seismic and electrical data applied to alpine permafrost

Coline Mollaret, Florian M. Wagner, Christin Hilbich, and Christian Hauck

Quantification of ground ice is particularly crucial for understanding permafrost systems. The volumetric ice content is however rarely estimated in permafrost studies, as it is particularly difficult to retrieve. Geophysical methods have become more and more popular for permafrost investigations due to their capacity to distinguish between frozen and unfrozen regions and their complementarity to standard ground temperature data. Geophysical methods offer both a second (or third) spatial dimension and the possibility to gain insights on processes happening near the melting point (ground ice gain or loss at the melting point). Geophysical methods, however, may suffer from potential inversion imperfections and ambiguities (no unique solution). To reduce uncertainties and improve the interpretability, geophysical methods are standardly combined with ground truth data or other independent geophysical methods. We developed an approach of joint inversion to fully exploit the sensitivity of seismic and electrical methods to the phase change of water. We choose apparent resistivities and seismic travel times as input data of a petrophysical joint inversion to directly estimate the volumetric fractions of the pores (liquid water, ice and air) and the rock matrix. This approach was successfully validated with synthetic datasets (Wagner et al., 2019). This joint inversion scheme warrants physically-plausible solutions and provides a porosity estimation in addition to the ground ice estimation of interest. Different petrophysical models are applied to several alpine sites (ice-poor to ice-rich) and their advantages and limitations are discussed. The good correlation of the results with the available ground truth data (thaw depth and ice content data) demonstrates the high potential of the joint inversion approach for the typical landforms of alpine permafrost (Mollaret et al., 2020). The ice content is found to be 5 to 15 % at bedrock sites, 20 to 40 % at talus slopes, and up to 95 % at rock glaciers (in good agreement to the ground truth data from boreholes). Moreover, lateral variations of bedrock depth are correctly identified according to outcrops and borehole data (as the porosity is also an output of the petrophysical joint inversion). A time-lapse version of this petrophysical joint inversion may further reduce the uncertainties and will be beneficial for monitoring and modelling studies upon climate-induced degradation.

 

References:

Mollaret, C., Wagner, F. M. Hilbich, C., Scapozza, C., and Hauck, C. Petrophysical joint inversion of electrical resistivity and refraction seismic applied to alpine permafrost to image subsurface ice, water, air, and rock contents. Frontiers in Earth Science, 2020, submitted.

Wagner, F. M., Mollaret, C., Günther, T., Kemna, A., and Hauck, C. Quantitative imaging of water, ice, and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data. Geophysical Journal International, 219 (3):1866–1875, 2019. doi:10.1093/gji/ggz402.

How to cite: Mollaret, C., Wagner, F. M., Hilbich, C., and Hauck, C.: Quantification of ground ice through petrophysical joint inversion of seismic and electrical data applied to alpine permafrost, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7489, https://doi.org/10.5194/egusphere-egu2020-7489, 2020.

EGU2020-8076 | Displays | CR4.2

Long-term energy balance measurements at three different mountain permafrost sites in the Swiss Alps

Martin Hoelzle, Christian Hauck, Jeannette Noetzli, Cécile Pellet, and Martin Scherler

The surface energy balance is one of the most important influencing factors for the ground thermal regime. It is therefore crucial to understand the interactions of the individual heat fluxes at the surface and within the subsurface layers as well as their relative impacts. A unique set of high-altitude meteorological measurements has been analysed to determine the energy balance at three mountain permafrost sites in the Swiss Alps, where data is being collected since the late 1990s in collaboration with the Swiss Permafrost Monitoring (PERMOS). The three stations have a standardized equipment with sensors for four-component radiation, air temperature, humidity, wind speed and direction as well as ground temperatures and snow height. The three sites differ considerably by their surface and ground material composition ranging from a coarse blocky active layer above ice supersaturated permafrost at rock glacier Murtèl-Corvatsch to deeply weathered micaceous shales, which are covered by fine grained debris of sandy and silty material with a low ice content at the Northern slope of Schilthorn summit. The third site at the Stockhorn plateau shows intermediate ice contents and heterogeneous surface conditions with medium-size debris, fine grained material and outcropping bedrock. Ice content estimation and general ground characterisation are based on geophysical surveying and borehole drilling.

 

The energy fluxes are calculated based on around two decades of field measurements. While the determination of the radiation budget and the ground heat flux is comparatively straightforward (by the four-component radiation sensor and thermistor measurements within the boreholes, respectively), larger uncertainties exist for the determination of sensible and latent turbulent heat fluxes. They are therefore determined on the one hand by the bulk aerodynamic method using the bulk Richardson number to describe the stability of the surface layer relating the relative effects of buoyancy to mechanical forces and on the other hand by the bowen ratio method.

 

Results show that mean air temperature at Murtèl-Corvatsch (1997–2018, elevation 2600 m asl.) is –1.66°C and has increased by about 0.7°C during the observation period. The Schilthorn (1999–2018, elevation 2900 m asl.) site shows a mean air temperature of –2.48°C with a mean increase of 1.0°C and the Stockhorn (2003–2018, elevation 3400 m asl.) site shows lower air temperatures with a mean of –5.99°C with an increase of 0.6°C. Measured net radiation, as the most important energy input at the surface, shows substantial differences with mean values of 33.41 Wm-2 for Murtèl-Corvatsch, 40.65 Wm-2 for Schilthorn and 24.88 Wm-2 for Stockhorn. The calculated turbulent fluxes show values of around 7 to 12 Wm-2 using the bowen ratio method and 8 to 18 Wm-2 using the bulk method at all sites. Large differences are observed regarding the energy used for melting of the snow cover: at Schilthorn a value of 12.41 Wm-2, at Murtèl-Corvatsch of 7.31 Wm-2 and at Stockhorn of 3.46 Wm-2 is calculated reflecting the differences in snow height at the three sites.

How to cite: Hoelzle, M., Hauck, C., Noetzli, J., Pellet, C., and Scherler, M.: Long-term energy balance measurements at three different mountain permafrost sites in the Swiss Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8076, https://doi.org/10.5194/egusphere-egu2020-8076, 2020.

EGU2020-9106 | Displays | CR4.2 | Highlight

Recent ground thermal dynamics and variations in northern Eurasia

Liangzhi Chen, Juha Aalto, and Miska Luoto

Ground thermal regime in cold environments is key to understanding the effects of climate change on surface–atmosphere feedbacks. The northern Eurasia, covering over half of terrestrial areas north of 40°N, is sensitive to the ongoing climate change due to underlain permafrost and seasonal frost. Here, we quantify the recent ground thermal dynamics and variations over northern Eurasia by compiling measurements of soil temperature data over 457 sites at multiple depths from 1975-2016. Our analysis shows that the mean annual ground temperature has significant warming trends by 0.30–0.31 °C/decade at depths of 0.8, 1.6, and 3.2 m. We found that the changes in annual maximum ground temperatures were more pronounced than mean annual ground temperatures with a weakened warming magnitude (0.40 to 0.31°C/decade) from upper to lower ground. Our results also suggest the substantial differences in warming magnitudes through parameters and depths over different frost-related areas. The ground over continuous permafrost area warmed faster than non-continuous permafrost and seasonal frost areas in shallow ground (0.8 and 1.6 m depth) but slower in deeper ground (3.2 m). Our study highlights the varied ground temperature evolutions at multiple depths and different frost-related ground, suggesting the importance of separated discussions on different frost-affected ground in application and future research. Noteworthy, the results indicate that the significant ground warming can promote greenhouse gas emissions from soil to atmosphere, further accelerating climate change.

How to cite: Chen, L., Aalto, J., and Luoto, M.: Recent ground thermal dynamics and variations in northern Eurasia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9106, https://doi.org/10.5194/egusphere-egu2020-9106, 2020.

EGU2020-9534 | Displays | CR4.2

Why rock glacier deformation velocities correlate with both ground temperatures and water supply at multiple temporal scales

Robert Kenner, Luisa Pruessner, Jan Beutel, Philippe Limpach, and Marcia Phillips

Recent studies have highlighted water supply as a driving factor for rock glacier deformation velocities. In parallel, numerous observations of correlating mean annual air- or ground temperatures and rock glacier velocities have been reported. We investigated the connection between rock glacier temperatures and –hydrology and found that there is no contradiction between both hypotheses. We observed that water supply to the shear horizon of rock glaciers is highly correlated to their mean annual temperatures and – even more pronounced – to their temperatures during early winter. The rock glacier temperatures influence the amount of water supplied to the shear horizon to a lesser extent, but strongly determine the duration of the water supply. The main external influencing factor on rock glacier dynamics found next to atmospheric warming was early winter snow cover. Our results are based on deformation- and borehole temperature measurements of four Swiss rock glaciers.

How to cite: Kenner, R., Pruessner, L., Beutel, J., Limpach, P., and Phillips, M.: Why rock glacier deformation velocities correlate with both ground temperatures and water supply at multiple temporal scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9534, https://doi.org/10.5194/egusphere-egu2020-9534, 2020.

EGU2020-10325 | Displays | CR4.2

Modelling of long-term permafrost evolution in the discontinuous permafrost zone of North-West Siberia

Ekaterina Ezhova, Ilmo Kukkonen, Elli Suhonen, Olga Ponomareva, Andrey Gravis, Viktor Gennadinik, Victoria Miles, Dmitry Drozdov, Hanna Lappalainen, Vladimir Melnikov, and Markku Kulmala

The rate of climate warming in North-West Siberia is among the highest in the world and this trend is especially pronounced in summer [1]. Analysis of permafrost thermal conditions in this area provides plausible scenarios of permafrost degradation also elsewhere. An increase in the summer mean temperature together with the prolongation of the warm season results in the increase of the thawing degree-days enhancing thawing of permafrost. Here we present the results of decadal temperature observations from three boreholes near Nadym, North-West Siberia. We further use the results and the observed cryolithological structure of soils in two boreholes to model the long-term evolution of the deep permafrost under two climate scenarios, RCP2.6 (climate action, fast reduction of CO2 emissions) and RCP8.5 (‘business as usual’). Both borehole sites have a topmost high-porosity, high-ice content layer of peat which helps prolonging the degradation. The main difference between the boreholes is snow cover resulting from the difference of borehole positions (one is located on the top of the hill). Our results suggest that under RCP8.5 scenario permafrost will degrade in both boreholes. On the contrary, under RCP2.6 scenario permafrost will degrade in one borehole with the deeper snow cover, where it already shows the signs of degradation. For the other borehole, the model predicts that permafrost will not degrade within the next 300 years, although the permafrost temperatures are eventually above -1°C.

[1] Frey K.E. & Smith L.C. Recent temperature and precipitation increases in West Siberia and their association with the Arctic Oscillation. Polar Research 22(2), 287–300 (2003).

How to cite: Ezhova, E., Kukkonen, I., Suhonen, E., Ponomareva, O., Gravis, A., Gennadinik, V., Miles, V., Drozdov, D., Lappalainen, H., Melnikov, V., and Kulmala, M.: Modelling of long-term permafrost evolution in the discontinuous permafrost zone of North-West Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10325, https://doi.org/10.5194/egusphere-egu2020-10325, 2020.

EGU2020-10837 | Displays | CR4.2

Does shrubs growth in the high-Arctic lead to permafrost warming?

Florent Domine, Georg Lackner, Maria Belke-Brea, Denis Sarrrazin, and Daniel Nadeau

With climate warming shrubs can grow on high-Arctic tundra. This impacts many terms of the energy budget, resulting in a modification of the permafrost thermal regime. The summer surface albedo is decreased. The winter surface albedo is decreased because shrubs protrude above the snow. Winter conductive fluxes through the snow are reduced because shrubs trap snow, increasing snow depth. Shrubs also favor both snow melt in fall and spring and depth hoar formation in fall and winter, and both these factors affect snow thermal conductivity. Soil thermal properties may also be affected because of increased moisture.  We have measured many terms of the energy budget at Bylot Island, 73°N, Canada, at a herb tundra site and in a nearby large willow shrub patch. Monitored variables include radiation, snow and soil thermal conductivity and standard atmospheric variables. We observe that soil temperature at 15 cm depth is 1.5°C warmer under shrubs on a yearly average. The energetics of both sites are simulated using SurfexV8 including the detailed snow model Crocus. Combining observations and simulations indicates that the increased soil moisture under shrubs, by delaying  freezing by one month in fall, is an important factor in winter soil warming. Summer temperature is also markedly warmer under shrubs because of lower albedo and because the shrub understory is less insulating than on herb, which facilitates warming. These results show that investigating shrub impact using manipulations such as shrub removal is questionable because it does not restore pre-shrub understory and moisture.

How to cite: Domine, F., Lackner, G., Belke-Brea, M., Sarrrazin, D., and Nadeau, D.: Does shrubs growth in the high-Arctic lead to permafrost warming?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10837, https://doi.org/10.5194/egusphere-egu2020-10837, 2020.

EGU2020-12707 | Displays | CR4.2

Rock glacier impact on high-alpine freshwater chemistry

Ulrike Nickus, Hansjoerg Thies, Karl Krainer, and Richard Tessadri

Borehole soundings have revealed a warming of mountain permafrost of up to 1°C during recent decades. There is evidence that the increase in air temperature has favored the solute release from active rock glaciers, and pronounced changes in water quality of headwaters in the Alps have been described. Here, we report on solute concentrations of selected streams and springs in the vicinity of an active rock glacier in the Central European Alps (Lazaun, Italy). Stream water sampling started in 2007, and samples were analysed for major ions and heavy metals. We compare surface freshwaters of different origin and chemical characteristics, i.e. outflows of active and fossil rock glaciers, a spring emerging from a moraine and an ice glacier fed stream. Substance concentrations were highest in springs impacted by active rock glaciers, and dissolved ions increased up to a factor of 3 through the summer season. This pattern reflects a seasonally varying contribution to runoff by the melting winter snow pack, summer precipitation, baseflow and ice melt. Intense geochemical bedrock weathering of freshly exposed mineral surfaces, which are due to the downhill movement of the active rock glacier, is considered as a major reason for the high ion and metal concentrations in late summer runoff. In addition, solutes contained in the ice matrix of the rock glacier are released due to enhanced melting of rock glacier ice. On the contrary, minimum substance concentrations without any seasonal variability were found in the moraine spring.

How to cite: Nickus, U., Thies, H., Krainer, K., and Tessadri, R.: Rock glacier impact on high-alpine freshwater chemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12707, https://doi.org/10.5194/egusphere-egu2020-12707, 2020.

EGU2020-13137 | Displays | CR4.2 | Highlight

15 years of snow manipulation reveals huge impact on lowland permafrost and vegetation

Margareta Johansson, Jonas Åkerman, Gesche Blume-Werry, Terry V. Callaghan, Torben R. Christensen, Sylvain Monteux, and Ellen Dorrepaal

Snow depth increases observed and predicted in the sub-arctic are of critical importance for the dynamics of lowland permafrost and vegetation. Snow acts as an insulator that protects vegetation but may lead to permafrost degradation. In the Abisko area, in northernmost Sweden, there has been an increasing trend in snow depth during the last Century. Downscaled climate scenarios predict an increase in precipitation by 1.5 - 2% per decade for the coming 60 years. The observed changes in snow cover have affected peat mires in this area as thawing of permafrost, increases in active layer thickness and associated vegetation changes have been reported during the last decades. An experimental manipulation was set up at one of these lowland permafrost sites in the Abisko area (68°20’48’’N, 18°58’16’’E) 15 years ago, to simulate projected future increases in winter precipitation and to study their effect on permafrost and vegetation. The snow cover has been more than twice as thick in manipulated plots compared to control plots and it has had a large impact on permafrost and vegetation. It resulted in statistically significant differences in mean winter and minimum ground temperatures between the control and the manipulated plots. Already after three years there was a statistically significant difference between active layer thickness in the manipulated plots compared to the control plots. In 2019, the active layer thickness in the control plots were around 70 cm whereas in the manipulated plots it was 110 cm. The increased active layer thickness has led to surface subsidence due to melting of ground ice in all the manipulated plots. The increased snow thickness has prolonged the duration of the snow cover in spring with up to 22 days. However, this loss in early season photosynthesis was well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons in the manipulated plots. Eriophorum vaginatum is a species that has been especially favored in the manipulated plots. It has increased both in number and in size. Underneath the soil surface, the roots have also been affected. There has been a strong increase in total root length and growth in the active layer, and deep roots has invaded the newly thawed permafrost in the manipulated plots. The increased active layer thickness has also had an effect on the bacterial community composition in the newly thawed areas. According to past, century-long patterns of increasing snow depth and projections of continuing increases, it is very likely that the changes in permafrost and vegetation that have been demonstrated by this experimental treatment will occur in the future under natural conditions.

How to cite: Johansson, M., Åkerman, J., Blume-Werry, G., Callaghan, T. V., Christensen, T. R., Monteux, S., and Dorrepaal, E.: 15 years of snow manipulation reveals huge impact on lowland permafrost and vegetation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13137, https://doi.org/10.5194/egusphere-egu2020-13137, 2020.

EGU2020-13452 | Displays | CR4.2 | Highlight

How do microorganisms from permafrost soils respond to short-term warming?

Victoria Martin, Julia Wagner, Niek Speetjens, Rachele Lodi, Julia Horak, Carolina Urbina-Malo, Moritz Mohrlok, Cornelia Rottensteiner, Willeke a' Campo, Luca Durstewitz, George Tanski, Michael Fritz, Hugues Lantuit, Gustaf Hugelius, and Andreas Richter

Arctic ecosystems outpace the global rate of temperature increases and are exceptionally susceptible to global warming. Concerns are raising that CO2 and CH4 released from thawing permafrost upon warming may induce a positive feedback to climate change. This is based on the assumption, that microbial activity increases with warming and does not acclimate over time. However, we lack a mechanistic understanding of carbon and nutrient fluxes including their spatial control in the very heterogeneous Arctic landscape. The objective of this study therefore was to elucidate the microbial controls over soil organic matter decomposition in different horizons of the active layer and upper permafrost. We investigated different landscape units (high-centre polygons, low-centre polygons and flat polygon tundra) in two small catchments that differ in glacial history, at the Yukon coast, Northwestern Canada.

In total, 81 soil samples were subjected to short-term (eight weeks) incubation experiments at controlled temperature (4 °C and 14 °C) and moisture conditions. Heterotrophic respiration was assessed weekly, whereas physiological parameters of soil microbes and their temperature response (Q10) were determined at the end of the incubation period. Microbial growth was estimated by measuring the incorporation of 18O from labelled water into DNA and used to calculate microbial carbon use efficiencies (CUE). Microbial biomass was determined via chloroform fumigation extraction. Potential activities of extracellular enzymes involved in C, N, P and S cycling were measured using microplate fluorimetric assays.

Cumulative heterotrophic respiration of investigated soil layers followed the pattern organic layers > upper frozen permafrost > cryoturbated material > mineral layers in both catchments. Microbial respiration responded strongly in all soils to warming in all soils, but the observed response was highest for organic layers and cryoturbated material at the beginning and end of the experiment. Average Q10 values at the beginning of the experiment varied between 1.7 to 4.3 with differences between horizons but converged towards Q10 values between 2.0min to 2.9max after eight weeks of incubation. Even though microbial biomass C did not change with warming, microbial mass specific growth was enhanced in organic, cryoturbated and permafrost soils. Overall, warming resulted in a 65% reduced CUE in organic horizons.

Our results show no indication for physiological acclimatization of permafrost soil microbes when subjected to 8-weeks of experimental warming. Given that the duration of the season in which most horizons are unfrozen is rarely longer than 2 months, our results do not support an acclimation of microbial activity under natural conditions. Instead, our data supports the current view of a high potential for prolonged carbon losses from tundra soils with warming by enhanced microbial activity.

This work is part of the EU H2020 project “Nunataryuk”.

How to cite: Martin, V., Wagner, J., Speetjens, N., Lodi, R., Horak, J., Urbina-Malo, C., Mohrlok, M., Rottensteiner, C., a' Campo, W., Durstewitz, L., Tanski, G., Fritz, M., Lantuit, H., Hugelius, G., and Richter, A.: How do microorganisms from permafrost soils respond to short-term warming?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13452, https://doi.org/10.5194/egusphere-egu2020-13452, 2020.

EGU2020-13874 | Displays | CR4.2

Towards mechanical modeling of rock glaciers from modal analysis of passive seismic data

Antoine Guillemot, Laurent Baillet, Stéphane Garambois, Xavier Bodin, Éric Larose, Agnès Helmstetter, and Raphaël Mayoraz

Among mountainous landforms, rock glaciers are mostly abundant in periglacial areas, as tongue-shaped heterogeneous bodies. By measuring physical properties sensitive to useful hydro-mechanical parameters of the medium, a wide range of geophysical methods provides interesting tools to characterize and monitor rock glaciers at large scale(1). However, the need of high resolution temporal monitoring reduces the choice of such methods.

Passive seismic monitoring systems have the potential to overcome these difficulties, as recently shown on the Gugla rock glacier(2). Indeed, seismological networks provide continuous recordings of both seismic ambient noise and microseismicity. From spectral analysis, we track resonance frequencies and modal parameters that are directly linked to elastic properties of the system, which evolve according to its rigidity and its density(3)(4). Here, we propose to evaluate the potential of this methodology on two rock glaciers (Laurichard and Gugla) located in the Alps, at elevations where climatic forcing influences their internal structures and consequently their dynamics.

For both sites, we succeed in tracking and monitoring resonance frequencies of vibrating modes during several years. These frequencies show seasonal variations, indicating a freeze-thawing effect on elastic properties of the structure.

Assuming vibrating systems, we perform 2D mechanical modeling of rock glaciers, which fits well the recorded resonant frequencies. By modeling the increase of rigidity due to freezing in wintertime, seasonal variations are also mimicked. Differences between observed and modeled values, together with the variability of the results over sites, are discussed.

We finally compare the results of modal analysis with those from Ground Penetrating Radar surveys, in order to converge on a consistent view of these rock glaciers and their freeze-thawing cycles.

 

References

  • (1) Kneisel, C., Hauck, C., Fortier, R., Moorman, B., (2008). Advances in geophysical methods for permafrost investigations. Permafrost and Periglacial Processes 19, 157–178. https://doi.org/10.1002/ppp.616
  • (2) Guillemot A., Baillet L., Helmstetter A., Larose E., Garambois S., Mayoraz R., (2019). Seismic monitoring in the Gugla rock glacier (Switzerland): ambient noise correlation, microseismicity and modelling, Geophysical Journal International, submitted.
  • (3) Roux Ph., Guéguen Ph., Baillet L., Hamze A. (2014). Structural-change localization and monitoring through a perturbation-based inverse problem, The Journal of the Acoustical Society of America 136, 2586; https://doi.org/10.1121/1.4897403
  • (4) Larose E., C. S. (2015). Environmental seismology: What ca we learn on earth surface processes with ambient noise. Journal of Applied Geophysics, 116, 62-74.

How to cite: Guillemot, A., Baillet, L., Garambois, S., Bodin, X., Larose, É., Helmstetter, A., and Mayoraz, R.: Towards mechanical modeling of rock glaciers from modal analysis of passive seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13874, https://doi.org/10.5194/egusphere-egu2020-13874, 2020.

EGU2020-13906 | Displays | CR4.2

Monitoring permafrost changes in the Yangtze River source region of the Qinghai-Tibetan Plateau using differential SAR interferometry

Lingxiao Wang, Lin Zhao, Huayun Zhou, Shibo Liu, Xiaodong Huang, and Chong Wang

Qinghai-Tibet Plateau (QTP) has the largest high-altitude permafrost zone in the middle and low latitudes. Substantial hydrologic changes have been observed in the Yangtze River source region and adjacent areas in the early 21st century. Permafrost on the QTP has undergone degradation under global warming. The ground leveling observation site near Tangula (33°04′N, 91°56′E) located in the degraded alpine meadow indicates that the ground has subsided 50mm since 2011. The contribution of permafrost degradation and loss of ground ice to the hydrologic changes is however still lacking. This study monitors the permafrost changes by applying the Small BAseline Subset InSAR (SBAS-InSAR) technique using C-band Sentinel-1 datasets during 2014-2019. The ground deformation over permafrost terrain is derived in spatial and temporal scale, which reflects the seasonal freeze-thaw cycle in the active layer and long-term thawing of ground ice beneath the active layer. Results show the seasonal thaw displacement exhibits a strong correlation with surficial geology contacts. The ground leveling data is used to validate the ground deformation monitoring results. Then, the ground deformation characteristics are analyzed against the landscape units. Last, the long-term inter-annual displacement value is used to estimate the water equivalent of ground ice melting.

How to cite: Wang, L., Zhao, L., Zhou, H., Liu, S., Huang, X., and Wang, C.: Monitoring permafrost changes in the Yangtze River source region of the Qinghai-Tibetan Plateau using differential SAR interferometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13906, https://doi.org/10.5194/egusphere-egu2020-13906, 2020.

EGU2020-14047 | Displays | CR4.2

Permafrost monitoring by reprocessing and repeating historical geoelectrical measurements

Christian Hauck, Christin Hilbich, Coline Mollaret, and Cécile Pellet

Geophysical methods and especially electrical techniques have been used for permafrost detection and monitoring since more than 50 years. In the beginning, the use of Vertical Electrical Soundings (VES) allowed the detection of ice-rich permafrost due to the clear contrast between the comparatively low-resistive active layer and the high-resistive permafrost layer below. Only after the development of 2-dimensional tomographic measurement and processing techniques (Electrical Resistivity Tomography, ERT), in the late 1990’s, electrical imaging was widely applied for a large range of different permafrost applications, including ice content quantification and permafrost monitoring over different spatial scales. Regarding ERT monitoring, the comparatively large efforts needed for continuous and long-term measurements implies that there are still only few continuous ERT monitoring installations in permafrost terrain worldwide. One of the exceptions is a network of six permafrost sites in the Swiss Alps that have been constantly monitored in the context of the Swiss Permafrost Monitoring Network (PERMOS) since 2005, enabling the analysis of the long-term change in the ground ice content and associated thawing and freezing processes (Mollaret et al. 2019).

On the contrary, a much larger number (estimated to be > 500) of permafrost sites exist worldwide, where singular ERT (or VES) measurements have been performed in the past - many of them published in the scientific literature. These data sets are neither included in a joint database nor have they been analysed in an integrated way. Within a newly GCOS Switzerland-funded project we address this important historical data source. Whereas singular ERT data from different permafrost occurrences are not easily comparable due to the local influence of the geologic material on the obtained electrical resistivities, their use as baseline for repeated measurements and subsequent processing and interpretation in a climatic context is highly promising and can be effectuated with low efforts.

In this presentation we will show evidence that singular ERT surveys in permafrost terrain can indeed be repeated and jointly processed after long time spans of up to 20 years, yielding a climate signal of permafrost change at various sites and on different landforms. Examples are given from various field sites in Europe and Antarctica, and the results are validated with borehole data, where available. We believe that a joint international data base of historical ERT surveys and their repetitions would add an important data source available for permafrost studies in the context of climate change.

 

Mollaret, C., Hilbich, C., Pellet, C., Flores-Orozco, A., Delaloye, R. and Hauck, C. (2019): Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites. The Cryosphere, 13 (10), 2557-2578.

How to cite: Hauck, C., Hilbich, C., Mollaret, C., and Pellet, C.: Permafrost monitoring by reprocessing and repeating historical geoelectrical measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14047, https://doi.org/10.5194/egusphere-egu2020-14047, 2020.

Surface state information, derived from ASCAT microwave sensors (C-band scatterometer), were empirically linked to in-situ arctic ground temperature measurements. The resulting FT2T-regressionmodel was established using the sum of days of year frozen and in-situ mean annual ground temperatures, both at specific depths and years. Regionally, the model showed the best results in Scandinavia and northern Russia with less than 1°C difference to the in-situ data. Overall, the results were valid for most depths and regions, with a slight tendency for underestimation of the ground temperatures on the Eurasian continent (about -1°C) and an overestimation on the American continent up to 2 °C.  The most northern parts of Greenland, the Canadian High Arctic Islands and Alaska, however, showed a high positive bias of more than 10°C. Reasons for this overshooting include the limited amount of measurements in those regions, the oceanic influence and possibly snow cover effects. 
Due to the inaccessibility of many arctic regions, in-situ data availability is still sparse and if available not harmonized. We used the currently revised annual ground temperature dataset from CCI+ Permafrost, which combines in-situ data from the GTNP-database, RosHydroMet and additional regional arctic ground temperature datasets (e.g. Nordicana). The resulting determination coefficients of the FT2T-model showed 55% explained variance at shallow borehole-depths below 80cm and decrease with depth to around 25% at 20 meters. This suggests that the sum of frozen days of year delivers better result at shallow depths in the active layer than at the actual permafrost table. The RMSE showed a dependency on the spread of measurement stations considered in the model calibration step. The more input regions we could use, the larger the RMSE got due to the increase of variability in the input data. Inevitably, it’s the in-situ information which enables the translation between ground temperatures and microwave backscatter and thus it fundamentally affects the accuracy of the result.

How to cite: Kroisleitner, C., Bartsch, A., Heim, B., and Wiezorek, M.: The potential of satellite derived surface state to empirically estimate pan-arctic ground temperature at specific depths and the essential role of in-situ data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15162, https://doi.org/10.5194/egusphere-egu2020-15162, 2020.

EGU2020-18276 | Displays | CR4.2

THM Experiment for the Investigation of Freeze-Thaw Processes in Soils and Grouting Materials

Jan Christopher Hesse, Markus Schedel, Bastian Welsch, and Ingo Sass

Freeze-thaw processes induced in the vicinity of borehole heat exchangers (BHE) as a result of operating temperatures below 0 °C can significantly affect the compound structure consisting of the BHE pipes, the cement-based grouting material as well as the surrounding soil. The hydraulic integrity of such systems is not ensured anymore and its thermal efficiency could be impaired. However, the knowledge on freezing and thawing processes in porous media, such as the grout and unconsolidated rock materials, is still incomplete. The content of unfrozen water has a strong impact on material properties influencing the overall heat and mass transfer processes. Moreover, freezing strongly depends on various boundary conditions such as soil type or pore water chemistry. Accordingly, it is essential to have adequate information about the freezing interval for different boundary conditions, which describe the transition from pure liquid water to the ice phase and vice versa.

Therefore, a thermo-hydraulic-mechanical (THM) experiment has been developed and is used to gain a more detailed insight into freezing processes in artificial grouts and unconsolidated rock materials. It consists of a modified triaxial test system, which can carry cylindrical samples with a diameter of up to 100 mm and a height of up to 200 mm. A confining pressure of up to 16 bar can be gained by a plunger system. The confining pressure liquid (water-glycol-mixture) can be tempered down to -25 °C and is used to induce freezing conditions on the lateral surface of the sample. Mechanical parameters such as the freeze pressure are recorded by an axial load sensor and a displacement sensor. Besides, the radial deformation can be observed by the volume displacement of the confining liquid. Moreover, the hydraulic conductivity of the sample is determined according to DIN EN ISO 17892 (2019). The fluid temperatures during the flow-through experiment can be varied between 5 °C and 25 °C to represent natural groundwater temperatures. In addition to that, the freeze-thaw experiment is equipped with an ultrasonic measurement device: In the observed temperature range, the wave velocity in solid particles is constant and not affected by temperature changes. However, with descending temperature, the ice content increases, which leads to an improved cross-linking of the solid soil particles. As a consequence, the bulk P-wave velocity increases with decreasing unfrozen water content. Hence, this relationship can be used to determine the content of unfrozen water during a freeze-thaw cycle.

At this time, the first experiments are conducted with this novel device. Consequently, initial results will be presented at the conference. Moreover, the results of the THM experiments will be implemented in numerical models, which allow for an upscaling of the experimental findings to real scale applications.

How to cite: Hesse, J. C., Schedel, M., Welsch, B., and Sass, I.: THM Experiment for the Investigation of Freeze-Thaw Processes in Soils and Grouting Materials, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18276, https://doi.org/10.5194/egusphere-egu2020-18276, 2020.

EGU2020-18397 | Displays | CR4.2 | Highlight

Upscaling of geophysical measurements: A methodology for the estimation of the total ground ice content at two study sites in the dry Andes of Chile and Argentina

Tamara Mathys, Christin Hilbich, Cassandra E.M. Koenig, Lukas Arenson, and Christian Hauck

With climate change and the associated continuing recession of glaciers, water security, especially in regions depending on the water supply from glaciers, is threatened. In this context, the understanding of permafrost distribution and its degradation is of increasing importance as it is currently debated whether ground ice can be considered as a significant water reservoir and as an alternative resource of fresh water that could potentially moderate water scarcity during dry seasons in the future. Thus, there is a pressing need to better understand how much water is stored as ground ice in areas with extensive permafrost occurrence and how meltwater from permafrost degradation may contribute to the hydrological cycle in the region.

Although permafrost and permafrost landforms in the Central Andes are considered to be abundant and well developed, the data is scarce and understanding of the Andean cryosphere lacking, especially in areas devoid of glaciers and rock glaciers.

In the absence of boreholes and test pits, geophysical investigations are a feasible and cost-effective technique to detect ground ice occurrences within a variety of landforms and substrates. In addition to the geophysical surveys themselves, upscaling techniques are needed to estimate ground ice content, and thereby future water resources, on larger spatial scales. To contribute to reducing the data scarcity regarding ground ice content in the Central Andes, this study focuses on the permafrost distribution and the ground ice content (and its water equivalent) of two catchments in the semi-arid Andes of Chile and Argentina. Geophysical methods (Electrical Resistivity Tomography, ERT and Refraction Seismic Tomography, RST) were used to detect and quantify ground ice in the study regions in the framework of environmental impact assessments in mining areas. Where available, ERT and RST measurements were quantitatively combined to estimate the volumetric ground ice content using the Four Phase Model (Hauck et al., 2011). Furthermore, we developed one of the first methodologies for the upscaling of these geophysical-based ground ice quantifications to an entire catchment in order to estimate the total ground ice volume in the study areas.

In this contribution we will present the geophysical data, the upscaling methodology used to estimate total ground ice content (and water equivalent) of permafrost areas, and some first estimates of total ground ice content in rock glacier and rock glacier free areas and compare them to conventional estimates using remotely sensed data.

 

Hauck, C., Böttcher, M., and Maurer, H. (2011). A new model for estimating subsurface ice content based on combined electrical and seismic datasets, The Cryosphere, 5: 453-468.

How to cite: Mathys, T., Hilbich, C., Koenig, C. E. M., Arenson, L., and Hauck, C.: Upscaling of geophysical measurements: A methodology for the estimation of the total ground ice content at two study sites in the dry Andes of Chile and Argentina, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18397, https://doi.org/10.5194/egusphere-egu2020-18397, 2020.

Warming of mountain permafrost leads to growth of active layer thickness and reduction of rock wall stability. The subsequent increase of instable rock volumes can have disastrous or even fatal consequences, especially when cascading events are simultaneously triggered. This growth of climate-change-connected hazard, together with the recent increase of exposition of infrastructure and people, poses the alpine environments at a high risk, which needs to be monitored. Laboratory-calibrated Electrical Resistivity Tomography (ERT) has shown to provide a sensitive record for frozen vs. unfrozen conditions, presumably being the most accurate quantitative permafrost monitoring technique in permafrost areas where boreholes are not available.

The data presented here are obtained at the Steintälli ridge in Switzerland, which presents highly vulnerable permafrost conditions. A consistent 3D field set-up, the robust temperature calibration and the quantitative inversion scheme allow to compare measurements from the longest time series (2006-2019) of ERT in steep bedrock. A direct link to mechanical changes measured with tape extensometer is provided. Comparison of repeated hourly measurements as well as Wenner and Schlumberger arrays are also shown here, in order to increase the robustness of the delivered results.

Confirming the long-term observation from air temperatures, results from multiple parallel transects show an average resistivity reduction of 22%, concentrated at deeper layers of the permafrost lens. The permafrost area in the 3D cross sections also decreased from 30 to 10% (about 500 to 150m2 in our transects), with losses mainly localized on the south-east part of the study site, but in some cases also extending to the north face. 

How to cite: Scandroglio, R. and Krautblatter, M.: Climate-change-induced changes in steep alpine permafrost bedrock. 13 years of 3D-ERT at the Steintälli ridge, Switzerland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18808, https://doi.org/10.5194/egusphere-egu2020-18808, 2020.

EGU2020-19575 | Displays | CR4.2

Modelling water-related processes in rock wall permafrost

Florence Magnin, Jean-Yves Josnin, Ludovic Ravanel, and Philip Deline

Rock wall permafrost has been increasingly regarded since the early 2000s in reason of the growing frequency and magnitude of bedrock failures from mountain permafrost areas. One of the main current challenges to better assess its degradation and the failure mechanisms is the understanding of hydraulic processes, i.e. water infiltration and circulation in the fractures. Indeed, recent thermal and mechanical models have considered a homogeneous and ice-saturated rock medium, overlooking water-related processes which may act along fractures when water percolates. But observations of water stains alongside ice bodies in several rock fall scars point out the need to gain knowledge about such processes.

Recent development in numerical codes allow to fully couple thermal and hydraulic processes, and have so far mostly been used to investigate polar permafrost terrains. In this communication, we will present a first attempt to couple thermal and hydraulic processes in a numerical model of high-alpine bedrock permafrost. This entails designing a new modelling approach accounting for heterogeneous (fractured) and non-saturated areas in the rock medium, as well as water outlets and fracture intersections to permit water circulation. We implement Richards equations in the Finite Element simulation system Feflow (DHI-WASY) to model variably saturated flow and advective-conductive heat transports combined with phase change processes. We simulate heat and mass transports in a 2D geometry (vertical cross-section) reflecting the Aiguille du Midi settings (3842 m a.s.l., Mont Blanc massif, European Alps). The model is forced with climate time series partially constructed out of measured air temperature and assumptions about previous climate period. Steady freezing occurring between 1550 and 1850 AD (Little Ice Age) points out the role of fractures in the freezing rate, as fractures favor infiltration of cold water from the surface, acting as freezing corridors. Under thawing, water movements are enabled in the unfrozen upper parts of the model geometry through a partially saturated domain, whereas the lower part remains saturated. In the thawed zones, fractures that are not completely filled by ice can accelerate water circulation and create thawing corridors.

In this communication, we will present the modelling approach and the preliminary results. We will show that our numerical investigations bear strong potential to address thermal and mechanical effects of water infiltration (from snow melting and rain) and circulation in the frozen bedrock.

 

How to cite: Magnin, F., Josnin, J.-Y., Ravanel, L., and Deline, P.: Modelling water-related processes in rock wall permafrost , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19575, https://doi.org/10.5194/egusphere-egu2020-19575, 2020.

EGU2020-19984 | Displays | CR4.2

New multi-phase thermo-geophysical model: Validate ERT-monitoring & assess permafrost evolution in alpine rock walls (Zugspitze, German/Austrian Alps)

Tanja Schroeder, Riccardo Scandroglio, Verena Stammberger, Maximilian Wittmann, and Michael Krautblatter

In the context of climate change, permafrost degradation is a key variable in understanding rock slope failures in high mountain areas. Permafrost degradation imposes a variety of environmental, economic and humanitarian impacts on infrastructure and people in high mountain areas. Therefore, new high-quality monitoring and modelling strategies are needed.

Electrical Resistivity Tomography (ERT) is the predominant permafrost monitoring technique in high mountain areas. Its high temperature sensitivity for frozen vs. unfrozen conditions, combined with the resistivity-temperature laboratory calibration on Wettersteinkalk (Zugspitze) (Krautblatter et al. 2010) gives us quantitative information on site-specific rock wall temperatures (Magnin et al. 2015). Long-term ERT-Measurements (2007/2014 – now) were taken at the Kammstollen along the northern Zugspitze rock face. Two high-resistivity bodies along the investigation area reach resistivity values ≥104.5Ωm (−0.5 °C), indicating frozen rock, displaying a core section with resistivities ≥104.7Ωm (−2 °C) (Krautblatter et al., 2010). We can differentiate seasonal variability, seen by laterally aggrading and degrading marginal sections (Krautblatter et al., 2010) and singular effects due to environmental factors and extreme weather events.

Here, we present a new local high-resolution numerical, process-orientated thermo-geophysical model (TGM) for steep permafrost rock walls. The model links apparent resistivities, the ground thermal regime and meteorological forcings as seasonality and long-term climate change to validate the ERT and project future conditions. The TGM comprises a surface energy balance model, conductive energy transport, turbulent and seasonal heat fluxes (sensible, latent, melt and rain heat fluxes) including phase-change, as well as a multi-phase rock wall composition.

Finally, we can reproduce the natural temperature field in the rock wall, assess the spatial-temporal permafrost evolution in alpine rock walls, validate the ERT measurements via the new TGM and the applicability of the laboratory derived resistivity-temperature relationship by Krautblatter et al. (2010) for natural rock-wall conditions.

 

Krautblatter, M., Verleysdonk, S., Flores-Orozco, A. & Kemna, A. (2010): Temperature- calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps). J. Geophys. Res. 115: F02003.

Magnin, F., Krautblatter, M., Deline, P., Ravanel, L., Malet, E., Bevington, A. (2015): Determination of warm, sensitive permafrost areas in near-vertical rockwalls and evaluation of distributed models by electrical resistivity tomography. J. Geophys. Res. Earth Surf., 120, 745-762.

How to cite: Schroeder, T., Scandroglio, R., Stammberger, V., Wittmann, M., and Krautblatter, M.: New multi-phase thermo-geophysical model: Validate ERT-monitoring & assess permafrost evolution in alpine rock walls (Zugspitze, German/Austrian Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19984, https://doi.org/10.5194/egusphere-egu2020-19984, 2020.

EGU2020-20066 | Displays | CR4.2

Present state of marginal mountain permafrost in South Eastern Europe

Flavius Sirbu, Alexandru Onaca, Florina Ardelean, Brigitte Magori, and Petru Urdea

Permafrost exists in the highest mountains of SE Europe (South Carpathians, Rila, Pirin) in small isolated patches, where local topography and landforms provide conditions for winter ground cooling and for shading and ground thermal isolation during summer.

We present a summary of the present state of mountain permafrost in the study area by analyzing the results of ERT (electrical resistivity tomography) and GPR (ground penetrating radar) profiles together with thermal measurements of ground surface and air performed at the sites of documented permafrost occurrence. The results are put in context with recent climate evolution by a decade of thermal measurements in the South Carpathians and three years in the Rila and Pirin Mountains.

Despite differences in air temperature and snow cover timing and thickness the permafrost extent remains constant at the study sites. The active layer is thick (between 5-10 m), whereas the permanently frozen layers vary in thickness even for the same study site, and are relatively thin compared to sites located in the Alps or the Andes, indicating that the existing permafrost is in imbalance with the current climate. Snow cover is probably the most important factor in seasonal evolution, controlling both the winter cooling and the summer thermal decupling of ground and air temperature. Recent evolution shows a tendency of shifting the snow cover period with later deposit and later thaw which favors permafrost conditions. We also observe a significant difference between Southern Carpathians and Rila and Pirin mountains, with snow patches lasting until late summer, August or September, in the later.

However snow cover present strong local variations in terms of thickness and isolating proprieties which makes it the least study and least understood factor in mountain permafrost dynamics in SE Europe.

How to cite: Sirbu, F., Onaca, A., Ardelean, F., Magori, B., and Urdea, P.: Present state of marginal mountain permafrost in South Eastern Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20066, https://doi.org/10.5194/egusphere-egu2020-20066, 2020.

CR5.1 – Observing and modelling glaciers at regional to global scales

EGU2020-2642 | Displays | CR5.1

A new working group on the Regional Assessments of Glacier MAss Change (RAGMAC)

Michael Zemp, Matthias H. Braun, Alex S. Gardner, Bert Wouters, Geir Moholdt, and Regine Hock

Retreating and thinning glaciers are icons of climate change and impact the local hazard situation, regional runoff as well as global sea level. For past IPCC reports, regional glacier change assessments were challenged by the small number and heterogeneous spatio-temporal distribution of in situ measurement series and uncertain representativeness for the respective mountain range as well as by spatial limitations of current satellite altimetry (only point data) and gravimetry (coarse resolution). Towards IPCC SROCC, there have been considerable improvements with respect to available geodetic datasets. Geodetic volume change assessments for entire mountain ranges have become possible thanks to recently available and comparably accurate DEMs. At the same time, advances have been made in processing methods for radar altimetry (CryoSat-2 swath processing), as well as new spaceborne laser altimetry (ICESat-2) and gravimetry (GRACE-FO) missions are in orbit and about to release data products to the science community. This opens new opportunities for regional evaluations of results from different methods as well as for truly global assessments of glacier mass changes and related contributions to sea-level rise. At the same time, the glacier research and monitoring community is facing new challenges related to data size, formats, and availability as well as new questions with regard to best practises for data processing chains and for related uncertainty assessments.

In this PICO presentation, we introduce a new working group of the International Association of Cryospheric Sciences (IACS) on Regional Assessments of Glacier Mass Change (RAGMAC; https://cryosphericsciences.org/activities/wg-ragmac/). The overall goal of this working group (WG) is bringing together the research community that is assessing regional glacier mass changes from various observation technologies and to come up with a new consensus estimate of global glacier mass changes and related uncertainties. The WG is organized in three work packages, two related to different remote sensing technologies (WG1: glaciological and geodetic DEM-differencing methods, WG2: altimetry and gravimetry) and a third that aims at regional comparisons of corresponding results. Participation is open to everybody who is willing to actively contribute to one or several of these work packages.

How to cite: Zemp, M., Braun, M. H., Gardner, A. S., Wouters, B., Moholdt, G., and Hock, R.: A new working group on the Regional Assessments of Glacier MAss Change (RAGMAC), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2642, https://doi.org/10.5194/egusphere-egu2020-2642, 2020.

EGU2020-5579 | Displays | CR5.1

Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change

Ben Marzeion, Regine Hock, Brian Anderson, Andrew Bliss, Nicolas Champollion, Koji Fujita, Matthias Huss, Walter Immerzeel, Philip Kraaijenbrink, Jan-Hendrik Malles, Fabien Maussion, Valentina Radic, David Rounce, Akiko Sakai, Sarah Shannon, Roderik van de Wal, and Harry Zekollari

Glacier mass loss is recognized as a significant contributor to current sea-level rise. However, large uncertainties remain in projections of glacier mass loss on global and regional scales. We present an ensemble of 279 global-scale glacier mass and area change projections for the 21st century based on eleven glacier models using up to ten General Circulation Models (GCMs) and four Representative Concentration Pathways (RCPs) as boundary conditions. We partition the total uncertainty into the individual contributions caused by glacier models, GCMs, RCPs, and natural variability. We find that emission scenario uncertainty is growing throughout the 21st century, and is the largest source of uncertainty by 2100. The relative importance of glacier model uncertainty decreases over time, but it is the greatest source of uncertainty until the middle of this century. The projection uncertainty associated with natural variability is small on the global scale but has strong effects on small regional scales. The projected global mass loss by 2100 relative to 2015 (75±64 mm sea-level equivalent (SLE) for RCP2.6, 165±98 mm SLE for RCP8.5) is lower than, but within the uncertainty range of previous projections.

How to cite: Marzeion, B., Hock, R., Anderson, B., Bliss, A., Champollion, N., Fujita, K., Huss, M., Immerzeel, W., Kraaijenbrink, P., Malles, J.-H., Maussion, F., Radic, V., Rounce, D., Sakai, A., Shannon, S., van de Wal, R., and Zekollari, H.: Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5579, https://doi.org/10.5194/egusphere-egu2020-5579, 2020.

EGU2020-10947 | Displays | CR5.1

Towards a 3-D model for large-scale glacier simulations

Harry Zekollari, Heiko Goelzer, Frank Pattyn, Bert Wouters, and Stef Lhermitte

Glaciers outside the two major ice sheets are key contributors to sea level rise, act as important sources of freshwater, and have great touristic value. To simulate the temporal evolution of these ice masses at regional- to global scale, simplified models are typically used that rely on volume scaling approximations or parameterizations based on observed glacier changes. These approaches rely on minimal data and are fast, but they do not account for mass redistribution through ice flow. More recently, efforts have been undertaken to represent ice dynamical processes in flowline models that can be applied at large spatial scales. These flowline approaches represent the mass transfer within a glacier in a more realistic way, but fail at reproducing the evolution of large glaciers, which are typically not confined by the local topography and do not have a pronounced elongated shape as represented in flowline models.

Here we present our first efforts to develop a 3D coupled surface mass balance – ice flow model that can be used to model the temporal evolution of an ensemble of glaciers. The main goal of such a model is to be able to simulate the temporal evolution of glaciers with distinct shapes and situated in various climatic regimes in an automated way. By relying on a 3D model architecture we aim to better represent processes crucial for glacier evolution, such as glacier calving and convergent flow from several tributaries. Here, we will present first tests with a prototype version of the model by reproducing steady state geometries of selected glaciers, and by simulating the evolution of these ice bodies under idealised forcing scenarios.

How to cite: Zekollari, H., Goelzer, H., Pattyn, F., Wouters, B., and Lhermitte, S.: Towards a 3-D model for large-scale glacier simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10947, https://doi.org/10.5194/egusphere-egu2020-10947, 2020.

EGU2020-9330 | Displays | CR5.1

Early 21st-century glacier surface mass balance across High Mountain Asia derived from remote sensing

Evan Miles, Michael McCarthy, Amaury Dehecq, Marin Kneib, Stefan Fugger, and Francesca Pellicciotti

Glaciers in High Mountain Asia have experienced intense scientific scrutiny in the past decade due to their hydrological and societal importance. The explosion of freely-available satellite observations has greatly advanced our understanding of their thinning, motion, and overall mass losses, and it has become clear that they exhibit both local and regional variations due to debris cover, surging and climatic regime. However, our understanding of glacier accumulation and ablation rates is limited to a few individual sites, and altitudinal surface mass balance is essentially unknown across the vast region.

Here we combine recent assessments of ice thickness and surface velocity to correct observed glacier thinning rates for mass redistribution in a flowband framework to derive the first estimates of altitudinal glacier surface mass balance across the region. We first evaluate our results at the glacier scale with all available glaciological field measurements (27 glaciers), then analyze 4665 glaciers (we exclude surging and other anomalous glaciers) comprising 43% of area and 36% of mass for glaciers larger than 2 km2 in the region. The surface mass balance results allow us to determine the equilibrium line altitude for each glacier for the period 2000-2016.  We then aggregate our altitudinal and hypsometric surface mass balance results to produce idealised profiles for distinct subregions, enabling us to consider the subregional heterogeneity of mass balance and the importance of debris-covered ice for the region’s overall ablation.

We find clear patterns of ELA variability across the region.  9% of glaciers accumulate mass over less than 10% of their area on average for the study period. These doomed  glaciers are concentrated in Nyainqentanglha, which also has the most negative mass balance of the subregions, whereas accumulation area ratios of 0.7-0.9 are common for glaciers in the neutral-balance Karakoram and Kunlun Shan. We find that surface debris extent is negatively correlated with ELA, explaining up to 1000 m of variability across the region and reflecting the importance of avalanching as a mass input for debris-covered glaciers at lower elevations. However, in contrast with studies of thinning rates alone, we find a clear melt reduction for low-elevation debris-covered glacier areas, consistent across regions, largely resolving the ‘debris cover anomaly’.  

Our results provide a comprehensive baseline for the health of the High Asian ice reservoirs in the early 21st Century. The estimates of altitudinal surface mass balance and ELAs will additionally enable novel strategies for the calibration of glacier and hydrological models. Finally, our results emphasize the potential of combined remote-sensing observations to understand the environmental factors and physical processes responsible for High Asia’s heterogeneous patterns of recent glacier evolution.

How to cite: Miles, E., McCarthy, M., Dehecq, A., Kneib, M., Fugger, S., and Pellicciotti, F.: Early 21st-century glacier surface mass balance across High Mountain Asia derived from remote sensing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9330, https://doi.org/10.5194/egusphere-egu2020-9330, 2020.

EGU2020-4262 | Displays | CR5.1

Modelling regional- and global-scale glacier volume changes over the last millennium

David Parkes and Hugues Goosse

We demonstrate modelling of regional- and global-scale volume changes in glaciers over the last millennium with the Open Global Glacier Model (OGGM) - a glacier geometry and surface mass balance model in active development - using reconstructed climate data timeseries from a set of 6 GCMs. The goals are: 1) to better understand how well different longer-term (extending back to the pre-industrial period) climate datasets perform specifically in terms of their impact on glaciers; 2) to analyse the ability of OGGM to model glaciers over longer timescales while still capturing observed changes over the period of instrumental record; and 3) to determine which regions are better or worse suited to this type of modelling on large scales. A secondary goal is to understand the relative impact of precipitation and temperature - the two primary climate variables used to drive OGGM - on regional glacier volume over this time period, using synthetic climate inputs which isolate long-term trends from each variable individually. Modelling over this last millennium timescale is important due to the preponderance of available instrumental data being much more recent, with glacier models developed and calibrated using data that are mostly recorded in a period of pronounced global glacier retreat. Modelling periods that include both recent warming (and associated observed glacier retreat) and the preceding period that is without such globally coherent changes in climate provides a valuable test of glacier models, to ensure they can generate both relative stability in glacier geometry in stable climates with realistic variability and subsequent reduction in ice mass where appropriate in response to clearer recent temperature trends.

How to cite: Parkes, D. and Goosse, H.: Modelling regional- and global-scale glacier volume changes over the last millennium, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4262, https://doi.org/10.5194/egusphere-egu2020-4262, 2020.

 

Thick debris cover, greater than about 5 cm, insulates ice and reduces melt rates. Despite this melt-suppressing effect, glaciers often thin rapidly under thick debris cover. In High Mountain Asia, the European Alps, and Alaska many debris-covered and debris-free glacier tongues are thinning at similar rates (e.g., Kääb et al., 2012). This apparent paradox is known as the ‘debris-cover anomaly’ (Pellicciotti et al., 2015). Two mechanisms have been proposed to explain this behavior, which are not mutually exclusive. First, glacier thinning under thick debris is enhanced by melt hotspots (lakes, ice cliffs, and streams) within otherwise continuous debris cover. Second, the decline in ice flow from upglacier leads to thinning under thick debris (e.g., Vincent et al., 2016).

We propose a new mechanism to explain why thinning amplifies under thick debris. It appears that debris cover—through its affect on the melt patterncontrols glacier geometry (i.e., patterns of ice thickness and surface slope). A characteristic debris-perturbed driving stress pattern results which in turn controls where dynamical thinning amplifies, often in the upper reaches of debris-covered tongues. Our explanation is supported with data from a suite of glaciers in the Himalaya and with simulations from a numerical debris-covered glacier model responding to climate change (Anderson and Anderson, 2016).

In all numerical simulations, the zone of maximum glacier thinning initially occurs upglacier from the debris cover. This zone of maximum thinning then propagates downglacier into the debris-covered portion. We explain how this zone of maximum thinning can be spatially pinned and amplified at different locations relative to the terminus depending on debris thickness, bed slope, glacier size, and glacier topology. This seemingly paradoxical mechanism in which debris itself controls thinning under thick debris is further supported by an analysis of published thinning data from glaciers across High Mountain Asia.

How to cite: Anderson, L. and Scherler, D.: Thick debris paradoxically controls the ‘anomalous’ thinning of debris-covered glaciers in High Mountain Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19296, https://doi.org/10.5194/egusphere-egu2020-19296, 2020.

EGU2020-4977 | Displays | CR5.1

Comparison of methods for initialization of the Open Global Glacier Model (OGGM)

Larissa van der Laan, Julia Eis, Kristian Förster, and Ben Marzeion

In order to assess glacier mass balance on large temporal and/or spatial scales, numerical modelling is an essential tool, complementing ground observations and remote sensing methods. For a reliable simulation of a glacier’s development over time, knowledge of its initial state is fundamental. Attaining this information entirely through empirical evidence is impossible due to a lack of data, hence the need for alternative, numerical methods. In this study, three methods of varying complexity are applied to initialize the Open Global Glacier Model (OGGM) for 254 glaciers. These glaciers have a minimum of 5 years of in-situ mass balance observations, allowing for direct comparison with modelled values. The initialization methods comprise, in brief, i) a basic spin-up, starting from present-day conditions, running the model for 200 years with a random climate, representative of the period 1900-2000 ii) a cold climate spin-up, allowing the glacier to grow and create a more representative initial condition for e.g. the year 1901 and iii) a synthetic experiment based on present day glacier observations and past climate information, used to generate a large set of physically plausible initial states, which are then evaluated. Using each method, we reconstruct the glaciers’ initial states and set up a forward run from which to extract mass balance values over the time period 1970-2014, used for validation purposes. The overall aim is to identify an initialization approach that can be successfully applied to our current set of 254 glaciers, as well as areas with even sparser data available, expanding the range of scale for glacier modelling.

How to cite: van der Laan, L., Eis, J., Förster, K., and Marzeion, B.: Comparison of methods for initialization of the Open Global Glacier Model (OGGM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4977, https://doi.org/10.5194/egusphere-egu2020-4977, 2020.

EGU2020-4257 | Displays | CR5.1

Surface mass balance modeling of mountain glaciers in the Caucasus and in the High Mountain Asia

Oleg Rybak, Elena Rybak, Victor Popovnin, Afanasy Gubanov, Rysbek Satylkanov, Maria Shahgedanova, and Vassiliy Kapitsa

 

            The most significant quantity characterizing current state of a mountain glacier is its surface mass balance (SMB). SMB responds to changing climatic conditions and therefore determines present and future behavior of the glacier. Formulation of SMB in terms of a mathematical model allows better understanding complex processes of the atmospheric impact on glacier dynamics. After several decades of development, common universal modeling principles and approaches have been elaborated. At present, most of the newly developed models are quite similar with only varying details mostly concerning parameterization of heat fluxes.

SMB is an interplay between positive (accumulation) and negative (ablation) components. Ablation is formulated either using temperature-index (positive degree day) approach or surface energy balance calculation (or combination of both). Both these approaches are based on genuine physical principles and that is why they can be easily transformed into computational algorithms. Results of ablation model calculations are relatively easily constrained by observations. In contrast, evaluation of accumulation is much more dependent on poorly constrained factors such as local atmospheric circulation, snow-storm transport (including post-depositional) and avalanche feeding.

Our approach to simulate components of SMB is based on energy balance approach and emulation of meteorological conditions using a simple stochastic weather generator. To validate the model, we use observed SMB data from several mountain glaciers in different environmental conditions – Djankuat (Central Caucasus), Tuyuksu (Zailiyski Alatau), Sary-Tor and Karabatkak (Inner Tien Shan). Suggested approach allows to easily construct an ensemble of numerical experiments and implement Monte Carlo method for the SMB evaluation. This possibility is especially significant for simulation of future states of glaciers according to one or another climatic scenario on a coupled ice flow-SMB model.

The reported study was funded by RFBR, project number 20-05-00681 (“Evolution of glaciation of Inner Tien Shan under climate change and technogenic influence”)

How to cite: Rybak, O., Rybak, E., Popovnin, V., Gubanov, A., Satylkanov, R., Shahgedanova, M., and Kapitsa, V.: Surface mass balance modeling of mountain glaciers in the Caucasus and in the High Mountain Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4257, https://doi.org/10.5194/egusphere-egu2020-4257, 2020.

EGU2020-9589 | Displays | CR5.1

Calibrating a regional glacier model using post-LIA glacier length changes in the Alps

Matthias Dusch, Kurt Nicolussi, and Fabien Maussion

We present an approach to calibrate a regional glacier model based on the well observed period since the mid-19th century LIA maximum.
We chose 30 glaciers distributed across the entire European Alps with frequent length change observations in that period. These glaciers account for 25% of today's total glacier area in the Alps. We run simulations with the Open Global Glacier Model (OGGM, https://oggm.org) driven by HISTALP (http://www.zamg.ac.at/histalp) gridded climate data. To calibrate the glaciers individually, we vary three model parameters within a reasonable range: (i) a precipitation scaling factor governing average mass-turnover and mass-balance profiles, (ii) the ice creep parameter governing basal sheer stress and the dynamics of ice flow, and (iii) a constant mass balance perturbation applied to the yearly mass-balance. This results in  1365 unique parameter combinations which were tested for all glaciers. We chose individual parameter subsets for every glacier based on objective criteria minimizing the difference between modeled and observed length changes.

We find that there is no unique parameter combination satisfying our criteria for all glaciers. It is also challenging to identify an ideal parameter combination for each individual glacier, since there is a trade-off between reproducing variability (useful for paleo-climate interpretations) and reproducing observed length change (useful for projections and planing).
Furthermore, model and input data uncertainties are variable in time, leading to non-unique optimal parameter sets. Therefore, we rely on an ensemble of simulations consisting of the best runs with respect to multiple statistical measures. Together with a cross-validation procedure, the ensemble produces a probabilistic uncertainty range which can be applied to Holocene glacier reconstructions and future evolution scenarios.

How to cite: Dusch, M., Nicolussi, K., and Maussion, F.: Calibrating a regional glacier model using post-LIA glacier length changes in the Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9589, https://doi.org/10.5194/egusphere-egu2020-9589, 2020.

EGU2020-17711 | Displays | CR5.1

Predicting glacier mass balance by data assimilation from on-ice cameras

Johannes Landmann, Christophe Ogier, Matthias Huss, and Daniel Farinotti

With the widespread retreat of glaciers, concerns emerge for the availability of water resources. These concerns are largest for future dry spells, when runoff from other sources is low. In this context, mass balance estimates for time horizons from days to weeks might help to better manage water resources in alpine regions. Here, we obtain such estimates from a combined modelling and data assimilation approach. Starting with three glaciers with detailed monitoring in Switzerland, we extrapolate our signal to other unmeasured glaciers in the country.

For the mass balance modeling, an ensemble of four melt models is tuned to match semi-annual in-situ observations from the Glacier Monitoring Switzerland (GLAMOS) program. With this ensemble, we then infer mass balance for the observed glaciers. Three of the glaciers (Rhonegletscher, Findelgletscher and Glacier de la Plaine Morte) were equipped with on-ice cameras between mid-June and early October 2019. The cameras transmitted 352 daily point mass balance observations which we assimilate into our model results by employing a particle filter.

To transfer the mass balance information of the three well-observed glaciers to other glaciers in Switzerland, we make use of the strong spatial correlation of cumulative melt. In a workflow here termed “percentile extrapolation method”, first, all glaciers without direct mass balance measurements are calibrated based on geodetic mass balances covering the 1980-2010 period. To reduce the large uncertainty in calibration on geodetic mass changes, we first predict average mass balance model parameters for each glacier with a random forest regressor. Then, we tune these parameters to match the geodetic mass balance in a least squares minimization. As soon as a mass balance climatology for the past has been calculated with this calibration, we determine with which percentiles of this climatology the current year’s mass balance ensemble estimate overlaps at the well-observed glaciers. These percentiles are then extrapolated in space using inverse distance weighting and they are applied to the climatology of unmeasured glaciers. The procedure yields a mass balance estimate at every single day of a year for every Swiss glacier taking into account specific glacier characteristics.

We compare the assimilated camera mass balances with interpolated measurements from the GLAMOS program. First results indicate that for the annual mass balance, the camera data lower the mean absolute error to 0.19 m water equivalent (w.e.), from 0.36 m w.e for a model prediction without data assimilation. The standard deviation of the prediction ensemble is reduced by 0.37 m w.e. on average. A cross-validation using percentile extrapolation between the glaciers equipped with a camera shows that annual mass balance can be predicted within 0.27 m w.e.. The summer (May to September) melt of other glaciers in the GLAMOS program can be predicted with an absolute error of 0.07m w.e. (model: 0.27 m w.e). Our results indicate that the continuous monitoring of a few selected sites has the potential of strongly improving daily near real-time mass balance estimates at the regional scale.

How to cite: Landmann, J., Ogier, C., Huss, M., and Farinotti, D.: Predicting glacier mass balance by data assimilation from on-ice cameras, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17711, https://doi.org/10.5194/egusphere-egu2020-17711, 2020.

Significant seasonal changes in ice flow have been reported for outlet glaciers in Greenland. Understanding the mechanisms that control these rapid intra-annual changes in dynamics could potentially help to clarify Greenland's long-term evolution and climate change response.

In this study, we investigate seasonal changes in ice flow velocity in order to better understand the processes controlling them. We focus on 3 Greenlandic glaciers of different types: Russell which is a land-terminating glacier with speed ranging from 50 to 350 m/yr,  Upernavik Isstrøm which is a marine-terminating tidewater glacier with speeds up to 4 km/yr, and Petermann Gletscher that has a large ice shelf and with speed at the order of 1 km/yr. Since 2014, the number of spaceborne observations over the ice sheet has increased dramatically with the launch of Landsat-8, Sentinel-1 and -2, providing almost continuous monitoring of glacier dynamics.

Here, we develop an automatic processing chain to derive dense time series of surface ice flow from radar sensors, Sentinel -1a/b, and optical sensors, Landsat-7/8 and Sentinel-2, using speckle or feature tracking algorithms. We construct a post-processing analysis based on local polynomial regression to filter our multi-sensor time series and create a velocity database with high temporal resolution and reduced noise. The database allows us to reconstruct the continuous evolution of surface ice velocity with frequency intervals ranging from monthly for the entire glacial basin to weekly for the downstream parts. 

Using this methodology, we obtain velocity fields for 4 years between 2015 and 2019 of the entire basins of Russell, Upernavik and Petermann glaciers. Our results clearly show the seasonal variations in flow to which these glaciers are subjected. We analyze the average seasonal fluctuations during the 4 years, as well as particular behavior in different years. These results are then compared and discussed in relation to potential external forcings such as subglacial hydrology (change in basal friction), fluctuations in the ice front or grounding line positions (change in buttressing) and the presence of sea ice or ice melange in front of the glaciers. 

Finally, we conclude on the benefits of our post-processing approach for the analysis of dense ice flow time series and provide first insights on the causes of seasonal variations observed on these 3 glaciers.

How to cite: Derkacheva, A., Mouginot, J., Millan, R., and Gillet-Chaulet, F.: Processing and analysis of dense ice velocity time series to reconstruct seasonal fluctuations of 3 greenlandic glaciers : Russell Gletscher, Upernavik Isstrom, Petermann Gletscher., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-307, https://doi.org/10.5194/egusphere-egu2020-307, 2020.

EGU2020-1649 | Displays | CR5.1

Ice thickness, volume and subglacial relief of Ashuu-Tor, Bordu, Kara-Batkak and Golubina glaciers (Central-Asia) derived from GPR measurements and different approaching methods

Lander Van Tricht, Philippe Huybrechts, Jonas Van Breedam, Johannes Fuerst, Oleg Rybak, Rysbek Satylkanov, Bakyt Ermenbaev, Victor Popovnin, and Chloë Marie Paice

Glaciers in the Tien Shan (Central-Asia) mountains contribute a considerable part of the freshwater used for irrigation and households in the dry lowland areas of Kyrgyzstan and its neighbouring countries. Since the Little Ice Age, the total ice mass in this mountain range has been decreasing significantly. However, accurate measurements of the current ice volume and ice thickness distribution in the Tien Shan remain scarce, and accurate data is largely lacking at the local scale. In 2016, 2017 and 2019, we organized 1-month field campaigns in Central-Asia to sound the ice thickness of four different glaciers in the Tien Shan using a Narod ground penetrating radar (GPR) system.

Here, we present and discuss our in-situ ice thickness measurements of the four glaciers. We performed in total more than 1000 GPR soundings. We found a maximum ice thickness of 200 meters in the central part of the southern facing Ashuu-Tor glacier. On both Bordu and Golubina, we measured ice thicknesses up to 140 meters. Kara-Batkak was found to have the thinnest ice which is in agreement to the large average slope of this glacier. We extended all the ice thickness measurements to the entire glacier surfaces using three different methods based on the assumption of plastic flow (method 1) and the principle of mass conservation (method 2 & 3) and assessed their differences.

In this research, we show a detailed ice thickness distribution of Ashuu-Tor, Bordu, Golubina and Kara-Batkak glaciers. This can be used for glaciological modelling and assessing ice and water storage. We also point out the locations of potential lake formation in bedrock overdeepenings as a succession of glacier retreat.

How to cite: Van Tricht, L., Huybrechts, P., Van Breedam, J., Fuerst, J., Rybak, O., Satylkanov, R., Ermenbaev, B., Popovnin, V., and Paice, C. M.: Ice thickness, volume and subglacial relief of Ashuu-Tor, Bordu, Kara-Batkak and Golubina glaciers (Central-Asia) derived from GPR measurements and different approaching methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1649, https://doi.org/10.5194/egusphere-egu2020-1649, 2020.

CR5.2 – Modelling ice sheets and glaciers

EGU2020-6403 | Displays | CR5.2

FEM-modelling of ice dynamics without remeshing

Josefin Ahlkrona and Daniel Elfverson

The Finite Element Method (FEM) has become a popular method for numerical ice sheet modelling, partly due to its capability of representing complex geometries. However, there is a limit to just how complicated these geometries can be. In the presence of irregular geometries and moving boundaries like those appearing in glaciology, costly remeshing and low mesh quality may become issues. To overcome these problems, new unfitted sharp interface methods such as CutFEM are being developed by the FEM community. The CutFEM method allows for the boundary to cut through a mesh, without requiring the element nodes to be located on the boundary. In this way simple structured meshes can be used and remeshing is avoided while accuracy and stability is retained. We develop a CutFEM method for the full Stokes equations and apply it to a transient simulation of the Arolla Glacier with both no slip and partial slip conditions at the bed, using a level-set function to track the moving ice surface. We demonstrate accuracy of the method and discuss extensions to modelling ice shelves and moving grounding lines.

How to cite: Ahlkrona, J. and Elfverson, D.: FEM-modelling of ice dynamics without remeshing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6403, https://doi.org/10.5194/egusphere-egu2020-6403, 2020.

EGU2020-17864 | Displays | CR5.2

Stress and strain rate variations and strain localisation in ice: Another complexity to be considered apart from a simple enhancement factor

Paul D. Bons, Tamara de Riese, Enrique Gomez-Rivas, Albert Griera, Maria-Gema Llorens, and Ilka Weikusat

To describe the rheology of ice, it is customary to employ a flow law that relates the (differential) stress to the strain rate, typically as a function of temperature. The flow law thus predicts a single strain rate for a given stress and temperature. However, ice 1h is highly anisotropic when deforming by dislocation creep as is usually assumed to be the case in glaciers and polar ice sheets. Ice is effectively much softer in shearing parallel to the basal plane compared to deformation that requires activation of the non-basal crystallographic slip planes. Numerical simulation of ice deformation with the full-field crystal plasticity code (VPFFT, Lebensohn & Rollett, 2020) coupled with the numerical simulation platform Elle (Llorens et al., 2016) show that deformation in aggregates of ice grains is highly heterogeneous and typically shows strong strain heterogeneity and strain localisation in shear zones. This localisation remains when lattice rotation has resulted in a strong crystallographic preferred orientation (CPO) with basal planes all oriented approximately parallel to the shear plane in simple-shear deformation.

 

Plots of the differential stress versus strain rate of all points of the full field model at one point in time show a wide scatter within the polycrystal. Although most basal planes have an orientation close to optimal for slip along this plane, few, if any material points actually show a stress-strain rate state close to the one predicted by the flow law for basal glide. On the contrary, the hard non-basal slip planes contribute significantly to the overall deformation. Shear zones show a stronger alignment of basal planes than the surrounding material. However, differential stress tends to be highest inside these shear zones, suggesting that shear zones are not simply the result of the presence of "soft" ice.

 

The results give insight in the highly complex behaviour of the strongly anisotropic material ice. This complexity is insufficiently described with a simple enhancement factor. We discuss how this complexity may help explain variations in grain size and apparent strength found in deep drill cores in the polar ice sheets.

 

Lebensohn, R.A., Rollett, A.D. 2020. Spectral methods for full-field micromechanical modelling of polycrystalline materials. Computational Materials Science 173, 109336.

Llorens, G.-M., Griera, A., Bons, P.D., Lebensohn, R.A., Evans, L.A., Jansen, D., Weikusat, I. 2016. Full-field predictions of ice dynamic recrystallisation under simple shear conditions. Earth and Planetary Science Letters 450, 233-242.

How to cite: Bons, P. D., de Riese, T., Gomez-Rivas, E., Griera, A., Llorens, M.-G., and Weikusat, I.: Stress and strain rate variations and strain localisation in ice: Another complexity to be considered apart from a simple enhancement factor, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17864, https://doi.org/10.5194/egusphere-egu2020-17864, 2020.

EGU2020-12602 | Displays | CR5.2

Spontaneous Formation of Internal Shear Zone in Ice Flowing over a Topographically Variable Bed

Emma Weijia Liu, Ludovic Räss, Jenny Suckale, Frédéric Herman, and Yury Podladchikov

The transition from slow flow to rapid sliding is a noticeable feature of both ice sheets and outlet glaciers. Most existing models attempting to understand the complex physical transition processes assume an idealized model geometry with a flat bed. These models have shown that the onset of sliding entails basal refreezing, which in turn suppresses sliding. The theoretical difficulties in understanding sliding commencement in these process-based models contrast with the apparent ubiquity of the transition in the field. Here, we hypothesize that the presence of basal topography could resolve the inconsistency between model predictions and field observations.

We test our hypothesis by investigating the flow-to-sliding transition in a process-based model of ice flowing over bedrock with significant roughness. We assume that the bed is rigid and that the boundary condition at the bed is no-slip. We incorporate variations in basal topography into an iterative nonlinear Stokes solver for thermo-mechanically coupled ice deformation using the Immersed Boundary Method. This approach permits us to address the basal ice to bedrock transition with high accuracy and to study the impact of the shape of this transition zone.

Our results suggest that shear heating in the vicinity of pronounced roughness extends well into the bulk of the ice, leading to a spatially variable viscosity. These spatial variations in topography can therefore significantly impact the overall viscosity distribution in the ice. High shear strain rates localize at the tops of the bedrock topography. Thermo-mechanical feedback lead to the spontaneous formation of internal shear band over time, by connecting the topographic heights. The internal shear zone accommodates the majority of shear deformation, inducing a sliding motion of the upper part of the domain. Our results provide a process-based explanation of recently measured ice deformation data at the West margin of Greenland Ice Sheet (Maier et al. 2019). It is also consistent with the proposed existence of a radio-echo free zone located in the lowest hundreds of meters above bedrock (Drews et al. 2009, Fujita et al. 1999).

 

Maier, Nathan, et al. "Sliding dominates slow-flowing margin regions, Greenland Ice Sheet." Science advances 5.7 (2019): eaaw5406.

Drews, Reinhard, et al. "Layer disturbances and the radio-echo free zone in ice sheets." The Cryosphere 3 (2009): 195-203.

Fujita, Shuji, et al. "Nature of radio echo layering in the Antarctic ice sheet detected by a two‐frequency experiment." Journal of Geophysical Research: Solid Earth 104.B6 (1999): 13013-13024.

How to cite: Liu, E. W., Räss, L., Suckale, J., Herman, F., and Podladchikov, Y.: Spontaneous Formation of Internal Shear Zone in Ice Flowing over a Topographically Variable Bed, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12602, https://doi.org/10.5194/egusphere-egu2020-12602, 2020.

EGU2020-13248 | Displays | CR5.2

Assessing sliding relations for glacier slip over realistic bed topography

Christian Helanow, Neal Iverson, Jacob Woodard, and Lucas Zoet

Accuracy of prognostic ice-sheet models sensitively depend on the degree to which processes related to boundary conditions can be represented. In particular, the extent to which ice slides against and interacts with its substrate highly affects large-scale dynamics of ice sheets and glaciers. A process-based understanding of how basal drag and slip are related to conditions at the ice-bed interface, such as local bed topography, debris and subglacial hydrology, is therefore necessary to constrain ice-sheet response to a changing climate and associated sea-level rise.

We use a numerical model to simulate ice flow over a set of bed topographies of diverse morphological character; each model topography is the result of statistical analysis of a high-resolution digital elevation model of a glacier forefield, surveyed using ground-based LiDAR or drone-based photogrammetry. Allowing for ice-bed separation and water-filled cavities to form, we investigate the range of slip behavior by for each topography relating basal drag to slip velocity and water pressure and how this relation is affected by debris at the ice-bed interface.

Our results for realistic hard beds illustrate that there is an upper bound on the drag supported locally; this is in accordance with previous studies of hard-bedded slip over idealized two-dimensional topographies. The magnitude of this bound depends on the character of the bed, but is for the cases investigated only a fraction of the theoretical maximum and lower than values used in numerical ice-sheet models. However, the range of sliding velocities over which basal drag increases is for the considered topographies comparable to physically reasonable slip velocities, implying that substantial cavitation at the bed does not necessarily preclude a locally rate-strengthening slip relation. The presence of debris at the ice-bed interface influences the magnitude of the upper bound on the basal drag, broadening the range over which heuristic, rate-strengthening sliding relations commonly used in glacier-flow models can apply.

How to cite: Helanow, C., Iverson, N., Woodard, J., and Zoet, L.: Assessing sliding relations for glacier slip over realistic bed topography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13248, https://doi.org/10.5194/egusphere-egu2020-13248, 2020.

EGU2020-9629 | Displays | CR5.2

Changes to glacier friction law due to solid friction

Juan Pedro Roldan Blasco, Olivier Gagliardini, Florent Gimbert, Adrien Gilbert, and Christian Vincent

Theoretical laws for glacier friction over hard bedrocks rely on several assumptions. One fundamental assumption is that perfect sliding (no resistance to slip) occurs at the local scale between ice and bedrock, in which case friction only occurs at a mesoscale from ice flowing past bed irregularities - here called viscous friction. This assumption is however challenged by the numerous observations that glaciers carry debris at their basal layers, which can exert frictional resistance locally through solid-type friction between debris and rock. This is to be translated at a mesoscale as an additive frictional term to the law.
We study how the action of solid friction modifies the overall glacier basal friction by applying a simple effective-pressure dependant Coulomb friction law into a steady-state finite element model of a glacier over sinusoidal bedrock. We find that the viscous drag reaches the same maximum value regardless of whether there is local solid friction or not. However, we find that in the no-cavitation regime (low water pressures) the deformation-slip ratio near the bed is enhanced when solid friction occurs, although total slip is lower. As a result, the sliding parameter - ratio between viscous drag and slip - is no longer constant, as opposed to expected in a pure-sliding scenario. For high water pressures, the influence of solid friction becomes smaller and the law tends to the pure-sliding case. We propose a simple update to pure-sliding derived laws (Weertman, 1957; Fowler, 1981; Schoof, 2005; Gagliardini et al., 2007) to take into account this effect.

How to cite: Roldan Blasco, J. P., Gagliardini, O., Gimbert, F., Gilbert, A., and Vincent, C.: Changes to glacier friction law due to solid friction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9629, https://doi.org/10.5194/egusphere-egu2020-9629, 2020.

EGU2020-9631 | Displays | CR5.2

Glacial cycle ice-sheet evolution controlled by ocean bed properties

Clemens Schannwell, Reinhard Drews, Todd A. Ehlers, Olaf Eisen, Christoph Mayer, Mika Malinen, Emma C. Smith, and Hannes Eisermann

Shortcomings in the description of ice dynamics have been recognized as a major limitation for projecting the evolution of the Greenland and Antarctic ice sheets. If current sea-level rise rates continue unabated, up to 630 million people will be at annual flood risk by 2100; making improved ice-sheet model projections a priority and of high socio-economic impact. Since the boundary condition at the underside of the ice-sheet is poorly known, improving constraints on the basal ice/bed properties is essential for accurate prediction of ice-sheet stability and grounding line positions. Furthermore, the history of grounding-line positions since the Last Glacial Maximum has proven challenging to understand due to uncertainties in bed conditions. Here we use a 3D full-Stokes ice-sheet model to investigate the effect of differing ocean bed properties on ice-sheet advance and retreat over a glacial cycle of 40,000 years. We do this for the Ekström Ice Shelf catchment, East Antarctica. We find that predicted ice volumes differ by >50 % under almost equal forcing when comparing (low-friction) sediment-covered with (high-friction) crystalline ocean beds. Grounding-line positions differ by >100 % (49 km), show significant hysteresis, and migrate non-steadily in both scenarios with long quiescent phases disrupted by leaps of rapid migration. Our new modelling framework extends the applicability of 3D full-Stokes ice-sheet models by an order of magnitude to previous studies. The simulations predict evolution of two entirely different catchment geometries (namely thick and slow vs. thin and fast), triggered exclusively by variable ocean-bed properties. This highlights that constraints not only for the bathymetry but also its geological properties are urgently needed for predicting ice-sheet evolution and sea level change.

How to cite: Schannwell, C., Drews, R., Ehlers, T. A., Eisen, O., Mayer, C., Malinen, M., Smith, E. C., and Eisermann, H.: Glacial cycle ice-sheet evolution controlled by ocean bed properties , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9631, https://doi.org/10.5194/egusphere-egu2020-9631, 2020.

EGU2020-6974 | Displays | CR5.2

Contrasting response of West and East Antarctic ice sheets to Glacial Isostatic Adjustment

Violaine Coulon, Kevin Bulthuis, Sainan Sun, Konstanze Haubner, and Frank Pattyn

The Antarctic ice sheet (AIS) lies on a solid Earth that displays large spatial variations in rheological properties, with a thin lithosphere and low-viscosity upper mantle (weak Earth structure) beneath West Antarctica and an opposing structure beneath East Antarctica. This contrast is known to have a significant impact on ice-sheet grounding-line stability. Here, we embedded a modified glacial-isostatic ELRA model within an Antarctic ice sheet model that considers a weak Earth structure for West Antarctica supplemented with an approximation of gravitationally-consistent local sea-level changes. By taking advantage of the computational efficiency of this elementary GIA model, we assess in a probabilistic way the impact of uncertainties in the Antarctic viscoelastic properties on the response of the Antarctic ice sheet to future warming by using an ensemble of 2000 Monte Carlo simulations that span a range of plausible solid Earth structures for both West and East Antarctica.
We show that on multicentennial-to-millennial timescales, model projections that do not consider the dichotomy between East and West Antarctic solid Earth structures systematically overestimate the sea-level contribution from the Antarctic ice sheet because regional solid-Earth deformation plays a significant role in promoting the stability of the West Antarctic ice sheet (WAIS). However, WAIS collapse cannot be prevented under high-emissions climate scenarios. At longer timescales and under unabated climate forcing, future mass loss may be underestimated because in East Antarctica, GIA feedbacks have the potential to re-enforce the influence of the climate forcing as compared with a spatially-uniform GIA model. In this context, the AIS response might be an even larger source of uncertainty in projecting sea-level rise than previously thought, with the highest uncertainty arising from the East Antarctic ice sheet where the Aurora Basin is very GIA-dependent.

How to cite: Coulon, V., Bulthuis, K., Sun, S., Haubner, K., and Pattyn, F.: Contrasting response of West and East Antarctic ice sheets to Glacial Isostatic Adjustment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6974, https://doi.org/10.5194/egusphere-egu2020-6974, 2020.

Ice flow models based on the Shallow Ice Approximation (SIA) are among the most broadly used type of ice flow model thanks to their simplicity and low computational costs. One key problem of SIA-based models are the mass conservation issues that emerge within steep terrain. In more detail, at some grid cells more ice can removed within one time step than there is present leading to negative ice thicknesses. This issue becomes increasingly problematic with topographical steepness and model resolution. As high resolutions become more accessible with faster computers, mass conservation errors might become increasingly important in the future.

Here we present a new scheme for SIA models that are integrated explicitly forward-in-time centred-in-space, one of the most common implementation. We show that mass conservation can be restored by capping surface differences with the upstream ice thickness in the computation of surface gradients, given a time step is used that maintains numerical stability. This new scheme is simple, strictly mass conserving, and can be implemented vectorially resulting in compact and efficient codes. We demonstrate the functionality of our new scheme and show some practical applications.

 

How to cite: Imhof, M.: A new strictly mass conserving surface gradient calculation scheme for SIA-based ice flow models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7604, https://doi.org/10.5194/egusphere-egu2020-7604, 2020.

EGU2020-9658 | Displays | CR5.2

Increasing stable time step sizes in ice sheet modelling

Andre Löfgren and Josefin Ahlkrona

In order to understand the rate at which an ice sheet is losing mass one has to consider its dynamics. Ice is a very slow moving, highly viscous, non-newtonian fluid and as such is most accurately described by the full Stokes equation. Time dependence is taken into account by coupling the Stokes equation to the so called free surface equation, which describes how the free surface boundary of the ice sheet is advected due to the Stokes velocity field.

A problem with this system is that it is numerically quite unstable and has a very strict time step constraint, where very small time steps are needed in order to have a stable solver. This constitutes a severe limitation for making long term predictions as the expensive nonlinear Stokes equation has to be solved in each time step.

By adding an additional term to the weak form of the Stokes equation we achieve stability for time steps 10-20 times larger than without stabilization. This stabilization technique is straightforward to implement into existing code and does not result in significantly larger computation times or memory usage.

How to cite: Löfgren, A. and Ahlkrona, J.: Increasing stable time step sizes in ice sheet modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9658, https://doi.org/10.5194/egusphere-egu2020-9658, 2020.

EGU2020-10613 | Displays | CR5.2

The zero-ice ice-flow problem

G. Hilmar Gudmundsson

When modelling ice flow, one often encounters the situation where melt is applied over ice-free areas. For example, determining the terminus position of a glacier involves finding the locations where applied surface melt and ice flow produces areas of zero ice thickness. How to best deal numerically this situation without producing negative ice thickness is an open and unsolved problem. One approach is to impose positive ice-thickness constraints and reformulating the problem as a constrained optimisation problem using the active-set method. This approach is, for example, used in the ice flow model Úa.  I’ll provide an overview over the approach used in the model and explain some difficulties, and how these have been addressed, associated with the use of higher order elements where the sign of the Lagrange multipliers can not be used to identify the active set.

How to cite: Gudmundsson, G. H.: The zero-ice ice-flow problem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10613, https://doi.org/10.5194/egusphere-egu2020-10613, 2020.

EGU2020-10919 | Displays | CR5.2

The role of ocean circulation in the propagation of rifts on ice shelves.

Mattia Poinelli, Eric Larour, and Riccardo Riva

The break-up of large ice shelves and the associated loss of ice are thought to play a destabilizing role in the ice sheet dynamics. Although ice shelves are a substantial buttressing source in the stability of continental ice sheets, the propagation of large rifts eventually leads to the break-up of icebergs into the ocean. As consequence, this loss of ice would trigger further glacier acceleration and ice sheets retreat, destabilizing the ice cap. Retreat and collapse of ice sheets are also thought to be related to regional climate warming. Indeed, satellite observations suggest that a warming surrounding would induce the ice sheet to progressive thinning and weakening.

The prolongation of un-grounded ice into the ocean is often interrupted by the propagation of fractures that eventually separates large icebergs from the ice shelf. These fractures are called rifts and range from dimensions of 10 to 100 km. A recent example of such phenomena is the massive break-up of the Larsen C in July, 2017 which followed the disintegration of Larsen A in 1995 and the partial break-up of Larsen B in 2002. The tabular iceberg formed by Larsen C was limited by the propagation of a large rift that began in summer 2016, although the ice shelf had already been thinning since 1992.

Rift initiation and propagation are thought to be the result of glaciological and oceanographic sources that trigger ice to break. Nonetheless, exact mechanisms remain elusive. The on-going project focuses on ice-ocean interactions in ice shelves that accommodate rifts by using oceanographic models. The goal is to couple rift propagation and ocean circulation underneath ice cavities in order to infer how basal melting affects the development of rifts. The numerical framework is developed within the capabilities of the MITgcm. We aim to identify the sensitivity of propagation rate and opening rate of rifts to variations in the ocean circulation that have occurred during the separation of part of the ice shelf.

On a larger scale, we are interested in the role of rifting in the stability of Antarctic shelves. Therefore, we work toward a better understanding of which processes are involved in the triggering of rift propagation.

How to cite: Poinelli, M., Larour, E., and Riva, R.: The role of ocean circulation in the propagation of rifts on ice shelves., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10919, https://doi.org/10.5194/egusphere-egu2020-10919, 2020.

EGU2020-11658 | Displays | CR5.2

Simulation of Aurora basin, East Antarctic

Liyun Zhao, Yan Zhen, Rupert Gladstone, Thomas Zwinger, and John Moore

The Aurora basin includes several fast-flowing glaciers (e.g. Totten and Dalton) and has large subglacial areas below sea level, which makes its study an essential part of evaluating the stability of East Antarctic against ocean warming. We use the 3D full-Stokes ice flow model Elmer/Ice to investigate the dynamic processes taking place in this basin. The spatial pattern of basal friction is deduced by inverse method from observed surface velocity. Particular focus is in the thermal condition at the bedrock. We further project the evolution of this basin during the 21st century with parameterized sub-ice shelf melting based provided by high resolution ocean models.

How to cite: Zhao, L., Zhen, Y., Gladstone, R., Zwinger, T., and Moore, J.: Simulation of Aurora basin, East Antarctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11658, https://doi.org/10.5194/egusphere-egu2020-11658, 2020.

EGU2020-11788 | Displays | CR5.2

Modeling fabric development using coupled non-parametric orientation and lattice strain-energy distribution functions

Nicholas Rathmann, Aslak Grindsted, Sérgio H. Faria, David A. Lilien, Christine S. Hvidberg, and Dorthe Dahl-Jensen

As polycrystalline ice undergoes ductile deformation, the c-axis fabric develops and the effective, macroscopic physical properties of ice become anisotropic. Modeling the flow of anisotropic ice therefore necessitates modeling the evolution of c-axes, too. We propose a non-parametric spectral model to account for the co-evolution of c-axis orientation distributions and stored lattice strain-energy distributions, which in principle allows any distribution shape to be represented. The coupled evolution provides the means to (statistically) model nucleation and migration recrystallization in an energy consistent way as nonuniform decay processes that depend on the accumulated cold work experienced by a given parcel of ice. The free model parameters determine the relative importance of grain rotation versus dynamic recrystallization processes given the local ice temperature, stress- and strain-rate states. We argue that the free parameters may be constrained by consulting the ice-core literature and present tentative simulations of the GRIP ice-core fabric.

How to cite: Rathmann, N., Grindsted, A., Faria, S. H., Lilien, D. A., Hvidberg, C. S., and Dahl-Jensen, D.: Modeling fabric development using coupled non-parametric orientation and lattice strain-energy distribution functions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11788, https://doi.org/10.5194/egusphere-egu2020-11788, 2020.

In winter 2014-2015 a long tunnel was dug into the ice cap Langjökull at about 1260 m a.s.l., close to the ELA. The tunnel was opened for tourists in spring 2015 (https://intotheglacier.is/) and has since then become a popular tourist attraction.  Before the tunnel was opened in winter 2015 and in the subsequent two years measurements of the tunnel deformation, temperature and density along the tunnel has been measured.  The tunnel is both closing because of ice deformation and it deforms with the glacier flow, which causes the entrance into the ice tunnel to become gradually steeper.  We use a full-Stokes ice flow model to compute the evolution of the tunnel floor and the closure of the tunnel. The deformation measurements are used to constrain the ice viscosity and the floor measurements to validate the modeled glacier flow. The model simulations are then used to predict the movement of the tunnel in the coming few years, which is useful for the planning of the tunnel entrance renovations.

How to cite: Aðalgeirsdóttir, G.: Modelling the deformation and movement of an ice tunnel in Langjökull ice cap, Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11964, https://doi.org/10.5194/egusphere-egu2020-11964, 2020.

EGU2020-18968 | Displays | CR5.2

A multi-approach skill-score procedure to optimize continental-scale ice-sheet models

Ilaria Tabone, Alexander Robinson, Jorge Alvarez-Solas, Javier Blasco, Daniel Moreno, and Marisa Montoya

Simulations of large-scale ice sheet models are crucial to understand the long-term evolution of an ice sheet and its response to climate forcings. However, solving the ice-flow equations and processes proper of the ice sheet at large spatial scales requires reducing the model computational complexity to a certain degree. To do so, coarse-resolution models represent several physical processes and ice characteristics through model parameterisations. Ice-sheet boundary conditions (e.g. basal sliding, surface ablation, grounded and marine basal melting) as well as unconstrained ice-flow properties (e.g. ice-flow enhancement factor) are some examples. However, choosing the best parameter values to well represent such processes is a demanding exercise. Statistical methods, from simple to advanced techniques involving Bayesian approaches, have been taken into account to evaluate the model performance. Here we optimise the performance of a new state-of-the-art hybrid ice-sheet-shelf model by applying a skill-score method based on a multi-misfits approach. A large ensemble of paleo-to-present transient simulations of the Greenland ice sheet (GrIS) is produced through the Latin Hypercube Sampling technique. Results are then evaluated against a variety of information, comprising the present-day state of the ice sheet (e.g. ice thickness, ice velocity, basal thermal state) as well as available paleo reconstructions (e.g. glacial maximum extent, past elevation at the ice core sites). Results are then assembled to generate a single skill-score value based on a gaussian approach. The procedure is applied to various model parameters to evaluate the best choice of values associated with their parameterisations. 

How to cite: Tabone, I., Robinson, A., Alvarez-Solas, J., Blasco, J., Moreno, D., and Montoya, M.: A multi-approach skill-score procedure to optimize continental-scale ice-sheet models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18968, https://doi.org/10.5194/egusphere-egu2020-18968, 2020.

EGU2020-2801 | Displays | CR5.2

Development of a numerical ice-sheet model for simulation of summit migration and dating

Fuyuki Saito, Ayako Abe-Ouchi, and Takashi Obase

Ice divides are important locations for deep drilling on ice-sheets.  Precise computation around a divide requires spatially very high resolution due to the characteristics of ice-flow around the divide.In addition, ice flow pattern is significantly different between an ice divide and the other areas: the flow around the divide requires more stress terms to compute than the other area.  Moreover, age computation around the summit is typical application of ice sheet models.  Performances of several numerical schemes, such as a higher-order upwind scheme or a semi-Lagrangian scheme, have been compared, however there are still some schemes not yet implemented and examined for this issue.

This study presents a recent development of Ice sheet model for Integrated Earth system Studies (IcIES) in particular, for improvement of dating scheme and inclusion of higher-order mechanics.

How to cite: Saito, F., Abe-Ouchi, A., and Obase, T.: Development of a numerical ice-sheet model for simulation of summit migration and dating, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2801, https://doi.org/10.5194/egusphere-egu2020-2801, 2020.

The Greenland ice sheet loses substantial amounts of mass, due to accelerating outlet glaciers and longer melting periods. Different positive feedback mechanisms, as the melt-elevation feedback and the ice-albedo feedback, introduce a non-linear evolution and may further accelerate mass loss. Negative feedbacks, such as the feedback between receding ice load and subsequent bedrock uplift, might counteract the accelerating positive feedbacks on long timescales. Roughly, the bedrock uplift amounts to 1/3 of the change in the ice sheet thickness on a timescale of millennia.

To explore the interplay of those feedbacks, we use simulations of the Greenland Ice Sheet with the Parallel Ice Sheet Model (PISM) including an Elastic Lithosphere Relaxing Asthenosphere (ELRA) model in an idealized warming scenario. In particular, we observe that depending on the temperature anomaly (and thus the retreat time) and the asthenosphere viscosity, three distinct responses of the ice sheet are possible:

How to cite: Zeitz, M., Haacker, J., and Winkelmann, R.: Ice load-bedrock uplift feedback leads to self-sustained oscillations in the Greenland Ice Sheet on long time scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22129, https://doi.org/10.5194/egusphere-egu2020-22129, 2020.

Understanding the anisotropic flow of ice is likely a key factor for the reliable prediction of the evolution of certain regions of the Earth’s ice sheets. Anisotropy of the crystal lattice alignment of ice grains is typically neglected in the large majority of ice-sheet models, however the viscosity of ice can vary by a factor of at least 9 in different directions, indicating the potential to provide a dominant control. Even though anisotropy can have a large regional influence, its effects are currently poorly understood. For example, it is an open question as to how different varieties of crystal fabrics are produced by different forms of deformation, and how these dynamics vary with temperature.

To address these questions, we use a continuum-mesoscopic approach, proposed by Faria (2006a) and Placidi (2010) to model the evolution of the ice crystallographic preferred orientations (CPOs). The model assumes strain induced crystal lattice rotation i.e. crystal plasticity with rigid body rotation where parameters representing the following processes are incorporated: the relative importance of basal slip, the magnitude of grain-boundary migration and the magnitude of rotation recrystallization. We solve the system using a new spectral method, which is computationally highly efficient, and able to fully resolve the multiple dimensions of the problem (time, space and the two dimensions of orientation angle). By considering the predictions of the model in the cases of deformation representing shear and compression, the model is determined to reproduce all the detail features observed in ice CPOs evolution such as secondary clusters or cone shapes. The results show excellent agreement with experiments of ice deformation in both shear and compression. The experimental comparison is used to determine the first constraints on three temperature-dependent dimensionless numbers defining the relative important of the recrystallization and slip processes. With these dependencies constrained using shear experiments, the application of the model results is able to reproduce the observations of crystal structure in compressive experiments with no further fitting parameters. The model is thus found to provide good agreement with laboratory experiments  across a range of temperatures, strain rates and flow fields.  Moreover, the predicted patterns correspond qualitatively to those observed in natural ice from cores, with our results providing the first theoretical demonstration of the characteristics of the fabric structure. 

How to cite: Richards, D., Pegler, S., Piazolo, S., and Harlen, O.: Evolution of crystallographic preferred orientations in flowing polycrystalline ice: A continuum modelling approach validated against laboratory experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13927, https://doi.org/10.5194/egusphere-egu2020-13927, 2020.

EGU2020-7038 | Displays | CR5.2

Sliding conditions beneath the Antarctic Ice Sheet

Rupert Gladstone, John Moore, Michael Wolovick, and Thomas Zwinger

Computer models for ice sheet dynamics are the primary tools for making future predictions of ice sheet behaviour, the marine ice sheet instability, and ice sheet contributions to sea level rise. However, the dominant mode of flow for ice streams is sliding at the bed, and the physical processes that control sliding are not well understood. Ice sheet models often use hard-bed (often Weertman-type) sliding rules for computational efficiency.  However, soft beds with deformable sediments, which are known from laboratory experiments and direct glacier observations to exhibit Coulomb plastic behaviour, are ubiquitous beneath fast flowing ice streams. Using hard-bed sliding rules leads to actively misleading rates of inland surface diffusion and grounding line migration as compared to plastic beds, leading to incorrect forecasts of future sea level rise. Here, we use a 3D Stokes-flow ice sheet model along with observations of the Antarctic Ice Sheet to infer, through inversions and steady temperature simulations, key basal properties, most important of which are sliding speed, basal resistance, friction heat and grounded ice basal melt rate.  In addition to simulations of the whole Antarctic Ice Sheet we implement fine resolution simulations of the Pine Island Glacier and its catchment.  Contrary to the predictions of most hard-bed sliding relations, we find no correlation between basal resistance and sliding speed for fast moving ice streams. These results emphasize the importance of Coulomb plastic sliding, and strongly suggest that ice sheet modelers should devote greater efforts to developing models that can incorporate Coulomb plastic sliding relations without generating numerical instabilities.  We use our model results, along with some assumptions, to infer properties of the sub-glacial hydrologic system.  Assumptions about connectivity of the sub-glacial hydrologic system to the ocean limit our capacity to assess sliding relations that incorporate a dependence on effective pressure, and likely cause underestimates of ice sheet mass loss in model-based predictions utilising such sliding relations.  Hydrology modelling is likely essential both to further assess sliding relations and to use sliding relations in future predictions.  We estimate that the dominant source of basal meltwater for Pine Island Glacier is due to friction heat caused by basal sliding, despite recent estimates of high heating due to volcanic activity.

 

How to cite: Gladstone, R., Moore, J., Wolovick, M., and Zwinger, T.: Sliding conditions beneath the Antarctic Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7038, https://doi.org/10.5194/egusphere-egu2020-7038, 2020.

EGU2020-1762 | Displays | CR5.2

Glacier sliding set by self-regulating feedback between friction and drainage efficiency

Adrien Gilbert, Florent Gimbert, Kjetil Thøgersen, Thomas Schuler, and Andreas Kääb

Glacier basal sliding accommodates most of glacier motion and is the main process behind glacier dynamic variability, able to substantially modulate glacier response to climate change. In particular, it controls glacier instabilities, surges, ice stream development and flow speeds of most glaciers on Earth. Paradoxically, glacier sliding remains one of the least understood processes in glacier physics due to the difficulty of accessing and observing the sub-glacial environment. In numerical models, sliding of glaciers is traditionally determined by friction laws interlinking basal shear stress, sliding velocity and water pressure. However, assessing the effects of water pressure on sliding remains a challenge due to the sparsity of appropriate data to validate coupled ice-flow/subglacial-hydrology models. We unify here the description of subglacial cavities transient dynamic for basal friction and sub-glacial hydrology and show how it interacts as a self-regulating coupled system. Our results are in striking agreement with observation from a unique multi-decadal record of basal sliding and water discharge in Argentière Glacier (French Alps). We show that sliding speed of hard-bedded glaciers is set by the drainage efficiency necessary to accommodate the melt water supply rather than being driven by water pressure. We suggest that liquid water supply at the glacier base rather water pressure should be used to develop friction laws that include the effect subglacial hydrology. This will make glacier dynamical response to climate change more predictable.

How to cite: Gilbert, A., Gimbert, F., Thøgersen, K., Schuler, T., and Kääb, A.: Glacier sliding set by self-regulating feedback between friction and drainage efficiency, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1762, https://doi.org/10.5194/egusphere-egu2020-1762, 2020.

EGU2020-21421 | Displays | CR5.2

Comparing the long-term fate of a snow cave and a rigid container buried at Dome C, Antarctica

Julien Brondex and Olivier Gagliardini

Ice Memory is an international project aiming at creating a global ice archive sanctuary in Antarctica. The design of a perennial subsurface storage space for the cores is a cornerstone of this project. Here, we use an ice/firn flow model to investigate possible storage solutions that would meet the specific requirements of the project. To this end, we consider two extreme cases in terms of rigidity of the facility: an ice cave dug into the firn and a perfectly rigid container buried within it. We focus on the rate of sinking of the facility as well as on the rate of closure of the cave and the evolution of the normal stresses supported by the container. Our results show that the lifetime of a cave is highly affected by the initial density of snow in its surrounding. On the other hand, the presence of the rigid container within the domain perturbs the flow of snow, creating patches of high density in its surrounding and leading to significant normal stresses on its walls. In particular, strong stress concentrations are obtained at the container angles. These results prove that unreinforced shipping containers are unsuited for this task.  

How to cite: Brondex, J. and Gagliardini, O.: Comparing the long-term fate of a snow cave and a rigid container buried at Dome C, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21421, https://doi.org/10.5194/egusphere-egu2020-21421, 2020.

EGU2020-8750 | Displays | CR5.2

Targeted Glacial Geoengineering through Seabed Anchored Curtains
not presented

Michael Wolovick, John Moore, Rajeev Jaiman, Jasmin Jelovica, and Bowie Keefer

Rapid sea level rise due to an ice sheet collapse has the potential to be extremely damaging to coastal communities and infrastructure, and conventional coastal protection techniques (dykes, levees, etc) can be quite expensive. In the past we have proposed that society might employ artificial sills and pinning points at critical marine ice streams in Antarctica to slow the rate of sea level rise at the source (Wolovick and Moore, 2018). However, thick earthen sills are likely to be extremely expensive and difficult to construct. If the goal of the intervention is only to block warm water from reaching the grounding line, then an alternate intervention consisting of thin flexible buoyant curtains anchored to the seabed might be employed instead. Flexible curtains are likely to be cheaper, more robust against iceberg collisions, and easier to remove in the event of unforeseen side effects. Here, we use a simple ice flow model to evaluate the effectiveness of such an intervention at three important Greenlandic outlet glaciers, and we make crude estimates of the forces on the curtain and of the likely cost of construction. We find that the single most important factor controlling the effectiveness of a thin water-blocking intervention (defined as either slowing glacier retreat or causing readvance) is the exposure of the glacier to deep warm water at the time of barrier construction. This means that, for Jakobshavn Isbrae, which has a deep (~1000 m) central trough extending well over 100 km inland, a water-blocking intervention is likely to be effective far into the future, and also that the preventable retreat (in comparison to a no-intervention scenario) is quite large. For Helheim and Kangerdlugssuaq, however, the central trough rises rapidly just a few tens of kilometers inland of the present-day calving front, removing the vulnerability to deep warm water after a relatively small retreat. This means both that the intervention must be begun relatively soon if it is to have an effect at those glaciers, and that the preventable retreat is smaller. With respect to the forces acting on the curtain, we find that the static tensile load on the curtain rises quadratically with the height above the seabed, and linearly with respect to the density contrast between the inner waters and the outer waters. Since the natural sills at the fjord mouths are roughly three times deeper at Helheim and Kangerdlugssuaq than they are at Jakobshavn, curtains at the former would need to be roughly an order of magnitude stronger than curtains at the latter. We estimate that this translates into roughly five times greater cost (per unit barrier length) at the two East Greenland glaciers than at Jakobshavn. Therefore, based on both cost and effectiveness, we find that this type of intervention is more favored for Jakobshavn than it is for Helheim and Kangerdlugssuuaq.

How to cite: Wolovick, M., Moore, J., Jaiman, R., Jelovica, J., and Keefer, B.: Targeted Glacial Geoengineering through Seabed Anchored Curtains, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8750, https://doi.org/10.5194/egusphere-egu2020-8750, 2020.

EGU2020-12802 | Displays | CR5.2

Identifying the the key factors of uncertainty in Helheim Glacier’s response to climate change

Mathieu Morlighem and Doug Brinkerhoff

Helheim Glacier is one of the largest glaciers in Greenland and, despite its importance, remains poorly understood. While this glacier has been relatively stable in the 1980s and 1990s, its terminus retreated dramatically by 6 km between 2001 and 2005. By 2006, the glacier stopped thinning, slowed down, and re-advanced 4 km and has been stable since 2007. Helheim is today the third fastest glacier of Greenland, reaching speeds >7 km/a, and drains a surface area of 50,000 km2. It is not clear how this glacier will change over the coming century and if another episode of exceptional retreat will occur in the very near future. We construct here a large ensemble of simulations of Helheim glacier over the next century, using a numerical model that includes a dynamic ice front forced by oceanic and atmospheric scenarios. This large ensemble allows to quantify the uncertainty in future retreat and mass loss, and also to attribute the fraction of mass loss uncertainty due to poorly constrained model parameters using main-effect Sobol indices for each input variable. This work helps determine the processes that affect projections the most and provide error bars on model projections.

How to cite: Morlighem, M. and Brinkerhoff, D.: Identifying the the key factors of uncertainty in Helheim Glacier’s response to climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12802, https://doi.org/10.5194/egusphere-egu2020-12802, 2020.

CR5.4 – Ice-sheet and climate interactions

EGU2020-15058 | Displays | CR5.4

Did a Beringian ice sheet once exist?

Zhongshi Zhang, Qing Yan, Ran Zhang, Florence Colleoni, Gilles Ramstein, Gaowen Dai, Martin Jakobsson, Matt O’Regan, Stefan Liess, Denis-Didier Rousseau, Naiqing Wu, Elizabeth J. Farmer, Camille Contoux, Chuncheng Guo, Ning Tan, and Zhengtang Guo

Did a Beringian ice sheet once exist? This question was hotly debated decades ago until compelling evidence for an ice-free Wrangel Island excluded the possibility of an ice sheet forming over NE Siberia-Beringia during the Last Glacial Maximum (LGM). Today, it is widely believed that during most Northern Hemisphere glaciations only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, recent recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf has triggered a new round of debate.These local glacial features, though often interpreted as local activities of ice domes on continental shelves and mountain glaciers on continents,   could be explained as an ice sheet over NE Siberia-Beringia. Only based on the direct glacial evidence, the debate can not be resolved. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to readdress the debate. Our simulations show that the paleoclimate records are not reconcilable with the established concept of Laurentide-Eurasia-only ice sheets. On the contrary, a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which well explains the climate records from around the North Pacific during the past four glacial-interglacial cycles. Our ice-climate modelling and synthesis of paleoclimate records from around the North Pacific argue that the Beringian ice sheet waxed and waned rapidly in the past four glacial-interglacial cycles and accounted for ~10-25 m ice-equivalent sea-level change during its peak glacials. The simulated Beringian ice sheet agrees reasonably with the direct glacial and climate evidence from Northeast Siberia-Beringia, and reconciles the paleoclimate records from around the North Pacific. With the Beringian ice sheet involved, the pattern of past NH ice sheet evolution is more complex than previously thought, in particular prior to the LGM.

How to cite: Zhang, Z., Yan, Q., Zhang, R., Colleoni, F., Ramstein, G., Dai, G., Jakobsson, M., O’Regan, M., Liess, S., Rousseau, D.-D., Wu, N., Farmer, E. J., Contoux, C., Guo, C., Tan, N., and Guo, Z.: Did a Beringian ice sheet once exist?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15058, https://doi.org/10.5194/egusphere-egu2020-15058, 2020.

EGU2020-5912 | Displays | CR5.4

Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial

Bas de Boer, Aurélien Quiquet, Pepijn Bakker, and Didier Roche

Glacial-interglacial changes of the Earth's climate are largely controlled by internal mechanisms that drive changes in greenhouse gases and ice sheets. In this study, we present model experiments of the penultimate deglaciation into the the last interglacial period, obtained with the Earth system model of intermediate complexity iLOVECLIM (v. 1.1.4). We show experiments with an imposed ice-sheet scenario together with initial results with both North and South interactive ice sheets using the GRISLI (v. 2.0) 3-D ice-sheet model. To this aim, we use a recently developed dynamical downscaling procedure to compute temperature and precipitation fields from the relative low resolution atmospheric model grid (T21, ~5.6º) to the GRISLI spherical grids of both the Northern Hemisphere and Antarctica (both 40 x 40 km). We investigate the separate impact of variations of greenhouse gases (GHG), orbital parameters and ice sheets on glacial-interglacial climate change over the past 240 kyr. Using prescribed greenhouse gases or ice sheets induce comparable changes in global mean temperature. Greenhouse gases, predominantly CO2, mainly have a global impact through radiative forcing on atmospheric temperatures. On the other hand, ice sheets have a more regional impact over the Northern Hemispheric (NH) continents and Antarctica during glacial times. Henceforth, polar amplification is more pronounced during glacial periods following large ice-sheet induced changes. Overall these results are comparable to other studies using a similar experimental design. In order to initiate the coupling between the ice sheets and climate model, we perform a large ensemble of experiments to calibrate ice-sheet model parameters for the present day. We will present how the optimal settings for the two ice-sheet regions are selected, based on a comparison with the present-day ice sheets on Antarctica and Greenland. For the coupling, iLOVECLIM generates downscaled SMB, surface temperatures, ocean temperature and salinity, and GRISLI provides surface elevation and ice extent, the coupling interval is 5 years. These experiments are started during the penultimate glacial maximum. We initialize the coupled iLOVECLIM - GRISLI experiments from a climatic forcing experiment using prescribed greenhouse gases and ice sheets, and generate a spin-up simulation of GRISLI using the optimal settings for three different time points at 136, 135 and 134 kyr ago. Initial experiments show a clear linkage between changes in ice sheets, sea ice and ocean circulation. Following the forced rise in atmospheric GHGs, the magnitude of retreat varries between ice sheets, related to location and insolation change (which increases for the NH but decreased for Antarctica). Moreover, sea ice both decrease following GHGs increase, and vary more in phase with global mean temperature.

How to cite: de Boer, B., Quiquet, A., Bakker, P., and Roche, D.: Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5912, https://doi.org/10.5194/egusphere-egu2020-5912, 2020.

EGU2020-2739 | Displays | CR5.4

Deglaciation of the Greenland and Laurentide ice sheets interrupted by glacier advance during abrupt coolings

Nicolas Young, Jason Briner, Gifford Miller, Alia Lesnek, Sarah Crump, Elizabeth Thomas, Simon Pendleton, Joshua Cuzzone, Jennifer Lamp, Susan Zimmerman, Marc Caffee, and Joerg Schaefer

The early Holocene (11.7 ka to 8.2 ka) represents the most recent period when the Laurentide and Greenland ice sheets underwent large-scale recession. Moreover, this ice-sheet recession occurred under the backdrop of regional temperatures that were similar to or warmer than today, and comparable to those projected for the upcoming centuries. Reconstructing Laurentide and Greenland ice sheet behavior during the early Holocene, and elucidating the mechanisms dictating this behavior may serve as a partial analog for future Greenland ice-sheet change in a warming world. Here, we use 123 new 10Be surface exposure ages from two sites on Baffin Island and southwestern Greenland that constrain the behavior of the Laurentide and Greenland ice sheets, and an independent alpine glacier during the early Holocene. On Baffin Island, sixty-one 10Be ages reveal that advances and/or stillstands of the Laurentide Ice Sheet and an alpine glacier occurred in unison around 11.8 ka, 10.3 ka, and 9.2 ka. Sixty-two 10Be ages from southwestern Greenland indicate that the GrIS margin experienced re-advances or stillstands around 11.6 ka, 10.4 ka, 9.1 ka, 8.1 ka, and 7.3 ka. Our results reveal that alpine glaciers and the Laurentide and Greenland ice sheets responded in unison to abrupt early Holocene climate perturbations in the Baffin Bay region. We suggest that during the warming climate of the early Holocene, freshening of the North Atlantic Ocean induced by a melting Laurentide Ice Sheet resulted in regional abrupt cooling and brief periods of ice-sheet stabilization superimposed on net glacier recession. These observations point to a negative feedback mechanism inherent to melting ice sheets in the Baffin Bay region that slows ice-sheet recession during intervals of otherwise rapid deglaciation.

How to cite: Young, N., Briner, J., Miller, G., Lesnek, A., Crump, S., Thomas, E., Pendleton, S., Cuzzone, J., Lamp, J., Zimmerman, S., Caffee, M., and Schaefer, J.: Deglaciation of the Greenland and Laurentide ice sheets interrupted by glacier advance during abrupt coolings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2739, https://doi.org/10.5194/egusphere-egu2020-2739, 2020.

Paleo reconstructions such as ice cores have revealed that the glacial period experienced frequent climate shifts between warm interstadials and cold stadials. The duration of these climate modes varied during glacial periods, and that both the interstadials and stadials were shorter during mid-glacial compared with early glacial period. Recent studies showed that the duration of the interstdials was controlled by the Antarctic temperature through its impact on the Atlantic Meridional Overturning Circulation (AMOC). However, similar relation was not found for the stadials, suggesting that other climate factors (e.g., differences in ice sheet size, greenhouse gases and insolation) might have played a role. In this study, we investigate the role of glacial ice sheets on the duration of stadials. For this purpose, freshwater hosing experiments are conducted with an atmosphere-ocean general circulation model MIROC4m under early-glacial and mid-glacial conditions. Then, a sensitivity experiment is conducted modifying only the configuration of the ice sheets.  The impact of mid-glacial ice sheets on the duration of the stadials is evaluated by comparing the recovery time of the AMOC after the cessation of the freshwater forcing. We find that the expansion of glacial ice sheets during mid-glacial shortens the recovery time of the AMOC. Partially coupled experiments, which switch the surface winds between the two experiments, show that the differences in the surface wind cause the shorter recovery time under mid-glacial ice sheet. The wind shortens the recovery time by increasing the surface salinity and decreasing the sea ice at the deepwater formation region. Thus the results suggest that differences in the surface wind between mid-glacial and early glacial ice sheets play an important role in causing shorter stadials during mid-glacial period.

How to cite: Sherriff-Tadano, S. and Abe-Ouchi, A.: Impact of mid-glacial ice sheets on the recovery time of the AMOC: Implications on the frequent DO cycles during the mid-glacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7844, https://doi.org/10.5194/egusphere-egu2020-7844, 2020.

EGU2020-18683 | Displays | CR5.4

Modelling the surface mass balance of the Greenland Ice Sheet from 6000 BP to the year 2200

Uta Krebs-Kanzow, Shan Xu, Hu Yang, Paul Gierz, and Gerrit Lohmann

The surface mass balance scheme dEBM (diurnal Energy Balance Model) provides a novel interface between atmosphere and land ice for Earth System modelling, which is based on the energy balance of glaciated surfaces. In contrast to empirical schemes, dEBM accounts for changes in the Earth’s orbit and atmospheric composition. The scheme only requires monthly atmospheric forcing (precipitation, temperature, shortwave and longwave radiation and cloud cover) and is computationally inexpensive, which makes it particularly suitable to investigate the response of ice sheets to long term climate change.
Here, we analyze the surface mass balance of the Greenland Ice Sheet (GrIS)  based on a climate simulation which covers the last 6000 years and a climate projection which extends to the year 2200. We validate our results with recent surface mass balance estimates from observations and regional modelling. Our model results allow to compare two distinctly different warm periods: the Mid Holocene (approx. 6000 years before present), which is characterized by intensified summer insolation, and the next centuries,  which will be characterized by reduced outgoing long wave radiation. We also investigate whether the temperature - melt relationship, as used in empirical  schemes, remains stable under changing insolation and atmospheric composition.

Krebs-Kanzow, U., Gierz, P., & Lohmann, G. (2018). Brief communication: An ice surface melt scheme including the diurnal cycle of solar radiation. The Cryosphere, 12(12), 3923-3930.

How to cite: Krebs-Kanzow, U., Xu, S., Yang, H., Gierz, P., and Lohmann, G.: Modelling the surface mass balance of the Greenland Ice Sheet from 6000 BP to the year 2200, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18683, https://doi.org/10.5194/egusphere-egu2020-18683, 2020.

EGU2020-10601 | Displays | CR5.4

Greenland ice sheet contribution to 21st century sea level rise as modelled by the coupled CESM2.1-CISM2.1

Laura Muntjewerf, Michele Petrini, Miren Vizcaino, Carolina Ernani da Silva, Raymond Sellevold, Meike Scherrenberg, Katherine Thayer-Calder, Sarah Bradley, Jan Lenaerts, William Lipscomb, and Marcus Lofverstrom

With the Community Earth System Model version 2.1 (CESM2.1) interactively coupled to the evolving Greenland Ice Sheet as simulated by the Community Ice Sheet Model version 2.1 (CISM2.1), we examine the Greenland Ice Sheet (GrIS) mass balance. The model has been run for the period 1850-2100 with historical and SSP5-8.5 scenario forcing, contributing to the coupled experiments within the framework of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) (Nowicki et al., 2016).

CESM2.1-CISM2.1 simulates a relatively strong global warming signal and strong weakening of meridional overturning circulation by 2100 compared to CMIP5 models. In our projection, the GrIS contributes 23 mm sea-level equivalent by 2050, and 109 mm by 2100, to global mean sea level rise. The southern GrIS drainage basins contribute 73% of the mass loss by mid-century, but the contribution decreases to 55% by 2100, as surface runoff in the northern basins progressively increases.

How to cite: Muntjewerf, L., Petrini, M., Vizcaino, M., Ernani da Silva, C., Sellevold, R., Scherrenberg, M., Thayer-Calder, K., Bradley, S., Lenaerts, J., Lipscomb, W., and Lofverstrom, M.: Greenland ice sheet contribution to 21st century sea level rise as modelled by the coupled CESM2.1-CISM2.1 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10601, https://doi.org/10.5194/egusphere-egu2020-10601, 2020.

EGU2020-20368 | Displays | CR5.4

The North Atlantic Oscillation and the Greenland ice sheet in CMIP6

Ruth Mottram, Susann Ascheneller, Florian Sauerland, Rasmus Anker Pedersen, Peter Thejll, Peter Lang Langen, Fredrik Boberg, Martin Stendel, Nicolaj Hansen, and Shuting Yang
The North Atlantic Oscillation (NAO) is an important control on both northern European weather and Greenland ice sheet surface mass budget via the path of storm tracks that deliver precipitation, particularly in the winter, and by the strength and persistence of the Greenland blocking high that promotes melt in summer. Within CMIP5 models, atmospheric blocking was generally poorly represented regardless of location, we here examine an ensemble of 10 CMIP6 fully coupled earth system models (ESMs) that were available by Summer 2019 in order to examine if model improvements better represent the NAO in CMIP6.
We examine  temperature over Greenland and the north Atlantic region as well as NAO position, persistence and strength in winter and summer for each model in the historical scenario. No single model performs well on all characteristics but the UKESM and EC-EARTH3 perform the best when compared to the ERA5 climate reanalysis.
We also show how the NAO is expected to change in 8 of these models under different future climate scenarios.  The location of the Icelandic low in particular migrates northwards by varying amounts, likely related to Arctic sea ice changes within the models and with a consequent impact on precipitation.
Downscaling experiments carried out using the HIRHAM5 regional climate model over the Greenland ice sheet show the importance of accurately characterising the NAO in order to correctly  estimate both winter accumulation and summer melt and the combination that gives the ice sheet mass budget. Our study emphasises the importance of assessing a range of different climate and weather variables when selecting models to downscale for obtaining ice sheet mass balance. We also note that while some progress has been made in better representing atmospheric blocking in ESMs, largely down to higher resolution in atmospheric models, there is still a substantial improvement required before ESMs can be said to accurately characterise the climate of the North Atlantic region with consequent impacts on ice sheet surface mass budget projections.

How to cite: Mottram, R., Ascheneller, S., Sauerland, F., Anker Pedersen, R., Thejll, P., Lang Langen, P., Boberg, F., Stendel, M., Hansen, N., and Yang, S.: The North Atlantic Oscillation and the Greenland ice sheet in CMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20368, https://doi.org/10.5194/egusphere-egu2020-20368, 2020.

EGU2020-953 | Displays | CR5.4

Sensitivity of the last glacial inception to initial and boundary conditions: lessons from a coupled climate-ice sheet model

Shan Xu, Uta Krebs-Kanzow, Paul Gierz, and Gerrit Lohmann

EGU2020-5647 | Displays | CR5.4

A circumpolar coupled ocean – Antarctic ice sheet configuration for investigating recent changes in Southern Ocean heat content

Charles Pelletier, Lars Zipf, Konstanze Haubner, Hugues Goosse, Frank Pattyn, and Pierre Mathiot

From 2016 on, observed tendencies of Southern Ocean sea surface temperatures and Antarctic sea ice extent (SIE) have shifted from cooling down (with SIE increase) to warming up (SIE decrease). This change of Southern Ocean surface thermal properties has been sustained since, which indicates that it is not solely due to the interannual variability of the atmosphere, but also to modifications in the ocean itself. Among other physical phenomena, the acceleration of continental ice shelf melt, through its subsequent impact on the Southern Ocean stratification, has been proposed as one of the potential meaningful drivers of the sea ice changes. Reciprocally, recent studies suggest that besides atmosphere forcings, the upper ocean thermal content bears significant impact on ice shelf melt rates and dynamics. Here we present a new circumpolar coupled Southern Ocean – Antarctic ice sheet configuration aiming at investigating the impact of this ocean – continental ice feedback, developed within the framework of the PARAMOUR project. Our setting relies on the ocean and sea ice model NEMO3.6-LIM3 sending ice shelf melt rates to the Antarctic ice sheet model f.ETISh v1.5, who in turn responds to it and provides updated ice shelf cavity geometry. Both technical aspects and first coupled results are presented.

How to cite: Pelletier, C., Zipf, L., Haubner, K., Goosse, H., Pattyn, F., and Mathiot, P.: A circumpolar coupled ocean – Antarctic ice sheet configuration for investigating recent changes in Southern Ocean heat content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5647, https://doi.org/10.5194/egusphere-egu2020-5647, 2020.

EGU2020-2272 | Displays | CR5.4

Transient Pleistocene simulations with a new coupled climate-ice-sheet model

Dipayan Choudhury, Axel Timmermann, Fabian Schloesser, and David Pollard

Orbital and COvariations over glacial timescales are widely held responsible as drivers of the ice-age cycles of the Pleistocene. Alongside these glacial cycles, our paleoclimate history is marked with abrupt changes and millennium scale variabilities. However, the relative contributions of these forcings over glacial transitions and mechanisms of abrupt changes are not very well understood. Here, using the recently developed three-dimensional coupled climate – ice-sheet model (LOVECLIM – Penn State University ice-sheet model), we simulate the glacial inception over the period of MIS7 to MIS6 (240-170ka). This period is the coldest interglacial post the Mid-Brunhes Event and includes one of the fastest glaciation/deglaciation events of the Late Pleistocene, over MIS7e-7d-7c (236-218ka); which we use here to benchmark our transient coupled model runs. Our results suggest that glacial inceptions are more sensitive to orbital variations, whereas terminations need both forcings to work in tandem over a tiny ablation zone at the southern margins of ice sheets. And abrupt changes may result from a critical interplay between the climate and the cryosphere systems. Using multiple ensembles in combination with conceptual dynamical systems’ models, we test the sensitivity of ice-sheets to various physical factors and discuss the presence of multiple equilibrium states and runaway effects. Additionally, our simulations show that regional scale variations at the southern end of Laurentide can lead to a bifurcation of the system and play a role even in orbital-scale ice-sheet growth/decay.

How to cite: Choudhury, D., Timmermann, A., Schloesser, F., and Pollard, D.: Transient Pleistocene simulations with a new coupled climate-ice-sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2272, https://doi.org/10.5194/egusphere-egu2020-2272, 2020.

EGU2020-16221 | Displays | CR5.4

Comparison of peri-Antarctic sub-shelf melt rates in coupled and uncoupled ice-sheet model simulations

Lars Zipf, Charles Pelletier, Konstanze Haubner, Sainan Sun, Hugues Goosse, and Frank Pattyn

Sub-shelf melting is the main driver of the mass loss of the Antarctic ice sheet. Various parametrizations exist to estimate basal melt rates within standalone ice sheet models, but they are not able to capture complex ocean circulation. Therefore, high resolution coupled ice sheet-ocean models are the ultimate approach to simulate observed sub-shelf melt rates on short time scales and thereby improve projections of future Antarctic sea level contribution.

Here, we present first results of a hindcast (last 30 years) of the new circumpolar coupled Southern Ocean – Antarctic ice sheet configuration, developed within the framework of the PARAMOUR project. The configuration, which captures whole Antarctica, is based on the ocean and sea ice model NEMO3.6-LIM3, providing the ice sheet model with monthly sub-shelf melt rates, and the Antarctic ice sheet model f.ETISh v1.5, providing the updated ice shelf cavity geometry to the ocean model. Different difficulties are tackled for the coupling: The initialisation of the ice sheet model is optimised for the chosen resolution of 8km, which is a tradeoff between capturing the main features for the peri-Antarctic setup and respecting the model purpose as fast ice sheet model. Framework conditions for the coupling, e.g. a constant ice-ocean mask, are tested and implemented. The optimal solution to estimate sub-shelf melt for small ice shelves that are not resolved in the ocean model due to the different resolution of the ice sheet and the ocean model, is investigated.
Sub-shelf melt rates of the coupled setup are compared to those modeled by the standalone ocean model and those of the standalone ice sheet model with different sub-shelf melt rate parametrizations (ISMIP6, plume, PICO, PICOP) and the sensitivity of the response of the ice sheet for the different basal melt rate patterns are investigated.

How to cite: Zipf, L., Pelletier, C., Haubner, K., Sun, S., Goosse, H., and Pattyn, F.: Comparison of peri-Antarctic sub-shelf melt rates in coupled and uncoupled ice-sheet model simulations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16221, https://doi.org/10.5194/egusphere-egu2020-16221, 2020.

EGU2020-5346 | Displays | CR5.4

Impacts of the PMIP4 ice-sheets on Northern Hemisphere climate during the last glacial period

Kenji Izumi, Paul Paul Valdes, Ruza Ivanovic, and Lauren Gregoire

The Last Glacial Maximum (LGM; 21,000 yr before present) is a target period of the paleoclimate simulations in the Coupled Model Intercomparison Project Phase 6 – the Paleoclimate Modeling Intercomparison Project Phase 4 (CMIP6-PMIP4) because of abundant paleoenvironmental data in continental, ice, and marine indicators. The LGM was a period of low atmospheric trace gases when large ice sheets covered over North America and Scandinavia. Paleoclimate reconstructions and modeling studies suggest that the Northern Hemisphere climate differed from today.

In this study, we used the coupled atmosphere and ocean model HadCM3B-M1 in order to investigate the impacts of the main LGM boundary condition changes, in particular, the ICE-6G_C, GLAC-1D, and PMIP3 ice-sheet reconstructions following the PMIP4 protocol, on the mean state of the climate over the Northern Hemisphere. First, we check the surface albedo forcing and feedback with a simplified partial derivative method and assess the surface temperature changes and their composition using a simple surface energy balance equation. Then, we investigate how patterns of stationary waves, westerly jet precipitation over the Northern Hemisphere change in response to the LGM ice-sheet configuration. Finally, we implement a paleo data-model comparison for validation of the large-scale climate changes over the Northern Hemisphere at the LGM. The wintertime stationary waves have the largest amplitude and different responses among the experiments, while stationary waves in summer are weak and similar responses. The LGM simulation with the ICE-6G_C better captures features of the LGM climate, but compared to the reconstructions, the climate model tends to overestimate cooling in summer and underestimate cooling in winter and simulate wetter conditions over the Northern Hemisphere.  

How to cite: Izumi, K., Paul Valdes, P., Ivanovic, R., and Gregoire, L.: Impacts of the PMIP4 ice-sheets on Northern Hemisphere climate during the last glacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5346, https://doi.org/10.5194/egusphere-egu2020-5346, 2020.

EGU2020-10255 | Displays | CR5.4

Coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module

Moritz Kreuzer, Ronja Reese, Willem Huiskamp, Stefan Petri, and Ricarda Winkelmann

Ocean-ice shelf interactions are the main drivers for the current mass loss from the Antarctic Ice Sheet. Recent studies have shown that increased continental meltwater input can enhance discharge through ice-ocean feedbacks. This raises the need for interactive modelling between ocean and ice-sheet systems to assess the consequences of additional freshwater input on the Antarctic region and beyond. While high-resolution simulations (1/4 degree or greater) can resolve detailed interactions between the ocean and ice shelf, the computational costs make them applicable only for regional studies or decadal to centennial time scales. In this study we present a framework for coupling a coarse resolution ocean model (MOM) to the Parallel Ice Sheet Model (PISM) via the Potsdam Ice-shelf Cavity mOdel (PICO). The intermediate model PICO approximates the overturning circulation in ice shelf cavities and includes ice-ocean boundary layer physics. We present this offline coupling approach and discuss the fluxes exchanged between the distinct model runs as well as energy and mass conservation. Using this flexible and computationally efficient framework, feedbacks between the ice and ocean can be analysed on a global spatial scale and paleoclimate time-scales.

 

How to cite: Kreuzer, M., Reese, R., Huiskamp, W., Petri, S., and Winkelmann, R.: Coupling the Parallel Ice Sheet Model with the Modular Ocean Model via an Antarctic ice-shelf cavity module, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10255, https://doi.org/10.5194/egusphere-egu2020-10255, 2020.

EGU2020-8205 | Displays | CR5.4

Warm Climate States during Last Glacial Cycle with a Multi-Resolution Climate/Ice Sheet Model

Paul Gierz, Lars Ackermann, Christian Rodehacke, Uta Krebs-Kanzow, Christian Stepanek, Dirk Barbi, and Gerrit Lohmann

Interglacials during the Quaternary represent the youngest climate states in the paleoclimate record that are similar to potential warmer-than-present states during the Anthropocene. In particular, those periods with warmer reconstructed temperatures and/or higher sea levels provide insights into the mechanisms that may be at work now and in the future. To date, climate model simulations of Quaternary Interglacials have been restricted to Atmosphere-Biosphere-Ocean simulations, with static ice sheet geometries from glaciological, geological, and geophysical reconstructions. Simulations including fully interactive ice sheets have not been widely available. Here, we present the first simulations of the PMIP4 timeslices for the Holocene and the Last Interglacial (LIG) with a fully coupled multi-resolution climate/cryosphere model, the AWI-ESM. We compare the simulated snapshots for the Holocene and LIG to simulations to proxy reconstructions, and to runs without dynamic ice sheets to highlight the processes now represented by the improved model. Furthermore, we show various schemes implemented in our model system to represent the ice sheet mass balance, both from surface ablation as well as ocean interaction. We find that both the Holocene and Last Interglacial ice sheets contain a smaller volume of ice compared to present day, with relative sea level equivalent changes of -3% and -7%, respectively.

How to cite: Gierz, P., Ackermann, L., Rodehacke, C., Krebs-Kanzow, U., Stepanek, C., Barbi, D., and Lohmann, G.: Warm Climate States during Last Glacial Cycle with a Multi-Resolution Climate/Ice Sheet Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8205, https://doi.org/10.5194/egusphere-egu2020-8205, 2020.

EGU2020-11625 | Displays | CR5.4

AMOC recovery in a multi-centennial scenario using a coupled atmosphere-ocean-ice sheet model

Lars Ackermann, Paul Gierz, and Gerrit Lohmann

Future global warming will affect ocean conditions by different mechanisms. One mechanism is the melting of the Greenland Ice Sheet (GIS), which may lead to a freshening of regions of deep water formation and eventually contribute to a possible slowdown of the Atlantic Meridional Overturning Circulation (AMOC). We simulate the two Coupled Model Intercomparison Project (CMIP) scenarios RCP4.5 and RCP8.5, to assess the effects of melt-induced fresh water on the AMOC. We use a newly developed coupled multi-resolution atmosphere-ocean-ice sheet model with high resolution at the coasts resolving the complex ocean dynamics. Our results show an AMOC recovery for both scenarios in simulations run with and without an included ice sheet model. We find that the ice sheet is not only acting as a source of freshwater to the ocean but also as a sink. This leads to local storage and redistribution of freshwater and largely compensates for the meltwater release. This physical consistency is missing in climate models without dynamic ice sheets. Therefore, we argue that freshwater hosing experiments should be assessed critically, as they might overestimate the North Atlantic freshening, induced by ice sheet melting. Because of the compensating effect, we find little effect of the included ice sheet model on the AMOC. Our results show a main freshwater release in West Greenland. There, the freshwater might be trapped in the Labrador Current and transported away from regions of deep water formation. Our results show an AMOC recovery, starting within the first half of the 22nd century. We assume the increase in net evaporation over the Atlantic and the resulting increase in ocean salinity, to be the main driver of this recovery.

How to cite: Ackermann, L., Gierz, P., and Lohmann, G.: AMOC recovery in a multi-centennial scenario using a coupled atmosphere-ocean-ice sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11625, https://doi.org/10.5194/egusphere-egu2020-11625, 2020.

EGU2020-11471 | Displays | CR5.4

A Gaussian process emulator for simulating ice sheet-climate interactions on a multi-million year timescale

Jonas Van Breedam, Philippe Huybrechts, and Michel Crucifix

Fully coupled state-of-the-art Atmosphere-Ocean General Circulation Models are the best tool to investigate feedbacks between the different components of the climate system on a decadal to centennial timescale. On millennial to multi-millennial timescales, Earth System Models of Intermediate Complexity are used to explore the feedbacks in the climate system between the ice sheets, the atmosphere and the ocean. Those fully coupled models, even at coarser resolution, are computationally very expensive and other techniques have been proposed to simulate ice sheet-climate interactions on a million-year timescale. The asynchronous coupling technique proposes to run a climate model for a few decades and subsequently an ice sheet model for a few millennia. Another, more efficient method is the use of a matrix look-up table where climate model runs are performed for end-members and intermediate climatic states are linearly interpolated.

In this study, a novel coupling approach is presented where a Gaussian Process emulator applied to the climate model HadSM3 is coupled to the ice sheet model AISMPALEO. We have tested the sensitivity of the formulation of the ice sheet parameter and of the coupling time to the evolution of the ice sheet over time. Additionally, we used different lapse rate adjustments between the relatively coarse climate model and the much finer ice sheet model topography. It is shown that the ice sheet evolution over a million year timescale is strongly sensitive to the choice of the coupling time and to the implementation of the lapse rate adjustment. With the new coupling procedure, we provide a more realistic and computationally efficient framework for ice sheet-climate interactions on a multi-million year timescale.

 

How to cite: Van Breedam, J., Huybrechts, P., and Crucifix, M.: A Gaussian process emulator for simulating ice sheet-climate interactions on a multi-million year timescale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11471, https://doi.org/10.5194/egusphere-egu2020-11471, 2020.

EGU2020-21261 | Displays | CR5.4

The ocean response to changes of the Greenland Ice sheet in a warming climate

Marianne S. Madsen, Shuting Yang, Christian Rodehacke, Guðfinna Aðalgeirsdóttir, Synne H. Svendsen, and Ida Margrethe Ringgaard

During recent decades, increased and highly variable mass loss from the Greenland ice sheet has been observed, implying that the ice sheet can respond to changes in ocean and atmospheric conditions on annual to decadal time scales. Changes in ice sheet topography and increased mass loss into the ocean may impact large scale atmosphere and ocean circulation. Therefore, coupling of ice sheet and climate models, to explicitly include the processes and feedbacks of ice sheet changes, is needed to improve the understanding of ice sheet-climate interactions.

Here, we present results from the coupled ice sheet-climate model system, EC-Earth-PISM. The model consists of the atmosphere, ocean and sea-ice model system EC-Earth, two-way coupled to the Parallel Ice Sheet Model, PISM. The surface mass balance (SMB) is calculated within EC-Earth, from the precipitation, evaporation and surface melt of snow and ice, to ensure conservation of mass and energy. The ice sheet model, PISM, calculates ice dynamical changes in ice discharge and basal melt as well as changes in ice extent and thickness. Idealized climate change experiments have been performed starting from pre-industrial conditions for a) constant forcing (pre-industrial control); b) abruptly quadrupling the CO2 concentration; and c) gradually increasing the CO2 concentration by 1% per year until 4xCO2 is reached.  All three experiments are run for 350 years.

Our results show a significant impact of the interactive ice sheet component on heat and fresh water fluxes into the Arctic and North Atlantic Oceans. The interactive ice sheet causes freshening of the Arctic Ocean and affects deep water formation, resulting in a significant delay of the recovery of the Atlantic Meridional Overturning Circulation (AMOC) in the coupled 4xCO2 experiments, when compared with uncoupled experiments.

How to cite: Madsen, M. S., Yang, S., Rodehacke, C., Aðalgeirsdóttir, G., Svendsen, S. H., and Ringgaard, I. M.: The ocean response to changes of the Greenland Ice sheet in a warming climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21261, https://doi.org/10.5194/egusphere-egu2020-21261, 2020.

EGU2020-19016 | Displays | CR5.4

Reconciling reconstructions and simulations of the Greenland ice sheet and its climate during the Last Interglacial period

Alexander Robinson, Emilie Capron, Jorge Alvarez-Solas, Michael Bender, Heiko Goelzer, and Marisa Montoya

There is still no consensus concerning the evolution of the Greenland ice sheet during the Last Interglacial period (LIG, 130-115 kyr ago). Ice cores indicate that the ice sheet survived over most of the continent. Proxy data indicate temperature anomalies of up to 6-8°C. However, under these conditions, models predict almost complete deglaciation. This paradox must be resolved to be able to quantify Greenland’s sea-level contribution during the LIG as well as to understand its sensitivity to future climate change. Here we analyze the available evidence and outline strategies to reconcile modeling and data efforts for Greenland during the LIG.

How to cite: Robinson, A., Capron, E., Alvarez-Solas, J., Bender, M., Goelzer, H., and Montoya, M.: Reconciling reconstructions and simulations of the Greenland ice sheet and its climate during the Last Interglacial period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19016, https://doi.org/10.5194/egusphere-egu2020-19016, 2020.

EGU2020-19692 | Displays | CR5.4

Coupled ice-climate simulation of future Greenland ice sheet evolution: mechanisms, thresholds and feedbacks for accelerated mass loss

Miren Vizcaino, Laura Muntjewerf, Raymond Sellevold, Carolina Ernani da Silva, Michele Petrini, Katherine Thayer-Calder, Meike Scherrenberg, Sarah Bradley, Jeremy Fyke, William Lipscomb, Marcus Lofverstrom, and William Sacks

The Greenland ice sheet (GrIS) has been losing mass in the last several decades, with a current contributing of around 0.7 mm per year to global mean sea level rise (SLR). Projections of future melt rates are often derived from standalone ice sheet models, forced by data from global or regional climate models. In many cases, the surface mass balance parameterization relies on simplified schemes that relate melt with surface temperature.

In this study, we present a mass and energy conserving, 350-year simulation with the Community Earth System Model version 2.1 (CESM2.1) bidirectionally coupled to the Community Ice Sheet Model version 2.1 (CISM2.1). In this simulation, the carbon dioxide concentration is initially increasing by 1% per year  from pre-industrial levels (287 ppmv), to a quadrupling (1140 ppmv) and stabilization after year 140. The model simulates a global warming of 5.3 K and 8.5 K with respect to preindustrial by years 131-150 and 331-150, respectively, and a strong decline in the North Atlantic Meridional Overturning Circulation that is initiated before GrIS runoff substantially increases. 91% of the total GrIS contribution to global mean sea level rise (SLR, 1140 mm) is simulated in the two centuries following CO2 stabilization, as the mass loss increases from 2.2 mm SLR per year in 131-150 to 6.6 mm SLR per year in 331-351. This increase is caused by melt acceleration as the ablation areas expand, and Greenland summer surface temperatures predominantly approach melt conditions when the global warming exceeds a certain threshold (around 4.2 K).  This enhances the albedo and turbulent heat fluxes contribution to total melt energy.  

How to cite: Vizcaino, M., Muntjewerf, L., Sellevold, R., Ernani da Silva, C., Petrini, M., Thayer-Calder, K., Scherrenberg, M., Bradley, S., Fyke, J., Lipscomb, W., Lofverstrom, M., and Sacks, W.: Coupled ice-climate simulation of future Greenland ice sheet evolution: mechanisms, thresholds and feedbacks for accelerated mass loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19692, https://doi.org/10.5194/egusphere-egu2020-19692, 2020.

EGU2020-16815 | Displays | CR5.4

Dynamic Hydrological Discharge and Lake Modelling for Coupled Climate Model Simulations of the Last Glacial Cycle

Thomas Riddick, Victor Brovkin, Stefan Hagemann, and Uwe Mikolajewicz

The continually evolving large ice sheets present in the Northern Hemisphere during the last glacial cycle caused significant changes to river pathways both through directly blocking rivers and through glacial isostatic adjustment. Associated with these changing river pathways was the formation and evolution of large glacial lakes such as Lake Agassiz. Studies have shown this changing hydrology had a significant impact on the ocean circulation through changing the pattern of freshwater discharge into the oceans. A coupled Earth system model (ESM) simulation of the last glacial cycle thus requires a hydrological discharge and lake model that uses a set of river pathways and lakes that evolve with Earth's changing orography while being able to reproduce the known present-day river network given the present-day orography. Here, we present a method for dynamically modelling rivers and lakes by applying predefined corrections to an evolving fine-scale orography (accounting for the changing ice sheets and isostatic rebound) each time the river directions and lakes basins are recalculated. The corrected orography thus produced is then used to create a set of fine-scale river pathways and these are then upscaled to a coarser scale on which an existing present-day hydrological discharge model within the JSBACH land surface model simulates the river flow. The associated glacial lakes are delineated from the same corrected fine scale orography; lake inflow and outflow being linked to the river flow model.

How to cite: Riddick, T., Brovkin, V., Hagemann, S., and Mikolajewicz, U.: Dynamic Hydrological Discharge and Lake Modelling for Coupled Climate Model Simulations of the Last Glacial Cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16815, https://doi.org/10.5194/egusphere-egu2020-16815, 2020.

We use the Community Earth System model 2.1 to investigate the response of the Greenland Ice sheet (GrIS) surface mass balance (SMB) to an idealized high CO2 forcing scenario (1% per year increase to four-times-preindustrial). The SMB calculation is coupled with the atmospheric model, using a physically-based surface energy balance scheme for melt, explicit calculation of snow albedo, and a realistic treatment of polar snow and firn compaction. The SMB becomes negative for a global mean temperature increase of 2.7 K compared to pre-industrial temperature, and the surface mass loss accelerates. Longwave radiation is the primary contributor to melt energy before acceleration. A decrease of the albedo due to ablation area expansion together with turbulent heat flux increase due to the surface of the ice sheet nearing melting point, are the main contributors at/after acceleration. Further, trends towards more positive North Atlantic Oscillation and more negative Greenland Blocking Index partially reduces future melt increase.

How to cite: Sellevold, R. and Vizcaino, M.: Greenland ice sheet surface mass balance response to high CO2 forcing: threshold and mechanisms for accelerated surface mass loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21686, https://doi.org/10.5194/egusphere-egu2020-21686, 2020.

EGU2020-17514 | Displays | CR5.4

A global ensemble-based comparison of the last two glacial inceptions with LCice 2.0

Marilena Geng, Lev Tarasov, and Taimaz Bahadory

What determines the character of glacial inceptions? Does the spatio-temporal pattern of ice nucleation and expansion vary much between Late Pleistocene glacial inceptions? According to various benthic del18O stacks, the MIS 7 interglacial was the most anomalous in character of the last 4 interglacials. Key differences include a weaker interglacial state and an initial fast inception interrupted by a return to a similar and extended interglacial state. These anomalies of MIS 7 along with temporal proximity arguably make the last two glacial inceptions the best test case for addressing our opening questions. As part of a larger project to generate and analyze a data-constrained ensemble of fully coupled ice/climate transient simulations for the last two complete glacial cycles, herein we present initial results comparing the last two glacial inceptions (MIS 7 and 5d). We are using a new version of the fully coupled ice/climate model LCice. LCice now simulates all 4 paleo ice sheet complexes with hybrid shallow-shelf and shallow-ice physics. It has already been shown to capture northern hemispheric ice sheet growth and subsequent retreat consistent with inferences from global mean sea level proxies (Bahadory et al, 2019). Orbital and greenhouse gas changes are the only external forcings applied to the model. A 300 member ensemble probes parametric uncertainties in both the 3D Glacial Systems Model and LoveClim (Atmosphere/Ocean/Vegetation) components of LCice. Our presentation will compare the evolution and relative phasing of all 4 paleo ice sheets, and associated changes in the rest of the modelled climate system.

How to cite: Geng, M., Tarasov, L., and Bahadory, T.: A global ensemble-based comparison of the last two glacial inceptions with LCice 2.0, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17514, https://doi.org/10.5194/egusphere-egu2020-17514, 2020.

EGU2020-10978 | Displays | CR5.4

The impact of inter-annual variability on the surface mass balance of Greenland

Tobias Zolles and Andreas Born

Surface mass balance models that are run over longer timescales are commonly forced with climatological forcing, disregarding natural climate variability. Here we investigate the impact of inter-annual variability of the present day climate using the energy balance model BESSI. The model is forced with daily data of precipitation, temperature, long and short wave radiation and humidity. We create synthetic time series of realistic climate forcing with different time scales of variability by re-ordering the years of present day reanalysis as well as using the climatology.

We find that the model significantly overestimates the Greenland SMB in case of climatological forcing when compared to the original daily reanalysis (40%). The effect of changing inter-annual variability by the re-ordering of forcing years has a relatively minor effect on the Greenland-wide mass balance (<5%), but is more important around the equilibrium line where positive feedback increase its impact over time. The averaging of precipitation is the key factor. It leads to a surface albedo increase as the nature of snowfall changes from event-based to continuous. To reduce this effect we use monthly climatologies in combination with a sub-monthly variability instead of daily climatologies, to retain the event (storm) based nature of precipitation.

Finally, we characterize the errors in cases of using climatology where interannual variability is unknown, such as simulations of the deep past and future and propose a solution.

How to cite: Zolles, T. and Born, A.: The impact of inter-annual variability on the surface mass balance of Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10978, https://doi.org/10.5194/egusphere-egu2020-10978, 2020.

CR5.7 – Ice shelves and tidewater glaciers - dynamics, interactions, observations, modelling

EGU2020-18499 | Displays | CR5.7

Dynamics of a barotropic current at an ice shelf front

Nadine Steiger, Elin Darelius, Satoshi Kimura, Ryan Patmore, and Anna Wåhlin

Ice shelves in West Antarctica are melting at an increasing rate due to the flow of relatively warm
Circumpolar Deep Water into the ice shelf cavities. The current that brings heat southward along the
eastern side of a trough towards an ice shelf front is found to have a barotropic and a baroclinic
component. Mooring observations in front of Getz Ice Shelf suggest that 90% (roughly 0.6 Sv) of the
volume transport and 65% of the temperature transport is linked to the barotropic component of the
current towards the ice shelf. It is unknown whether and how much of a barotropic current can
penetrate under the ice shelf across the about 300 m deep ice shelf front, where lines of constant water
column thickness discontinue.
We conduct idealized modelling with MITgcm to investigate the dynamics of a barotropic current at the
ice shelf front. Friction and strong vertical velocities at the ice shelf front break the potential vorticity
constraint and allow the flow to partly enter the ice shelf cavity. Only a small fraction of the current
penetrates deep into the cavity, while a strong current flows parallel to the ice shelf front, where basal
melt is largely enhanced. How much of the current enters the cavity and how far it reaches depends on
the ice shelf- and bedrock topography.

How to cite: Steiger, N., Darelius, E., Kimura, S., Patmore, R., and Wåhlin, A.: Dynamics of a barotropic current at an ice shelf front, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18499, https://doi.org/10.5194/egusphere-egu2020-18499, 2020.

EGU2020-15996 | Displays | CR5.7

Increased ice flow in the Getz region of West Antarctica, from 1994 to 2018

Heather Selley, Anna Hogg, Stephen Cornford, Andrew Shepherd, Pierre Dutrieux, Jan Wuite, Anders Kusk, Thomas Nagler, and Lin Gilbert

The Getz region is a marine-terminating sector of West Antarctica, characterised by a ~650 km long ice shelf that buttresses the inland ice sheet. The majority of the Getz drainage basin is grounded well below sea level, and while the ice shelf has thinned, its calving front has remained relatively stable since the early ’90s. Satellite observations have shown strong thinning of both the ice sheet and ice shelf over the past 25-years, and mass balance studies have shown that the sector is negatively imbalanced (−16.4 ± 4.0 Gt/year). In this study, we use satellite data to measure ice speed in the Getz region, over a 25-year period from 1994 to 2019. We use Synthetic Aperture Radar (SAR) data from historical missions including ERS-1, 2 and ALOS PALSAR, in combination with newer data from the Sentinel-1a & b satellite constellation, to generate annual velocity maps. The Sentinel-1 data extend the historical velocity record and provides a new high temporal resolution record, 6-day averaged solutions, of velocity change since 2017. We used satellite observations in combination with the BISICLES ice sheet model to fill gaps in the observational record, and to measure ice discharge and from the region. We find there are 14 distinct flow units that drain the Getz coastline, with average speeds ranging from 153 ± 7 to 1053 ± 194 m/yr around the grounding line. Our results show that all of these flow units have sped up during the study period, since 1994. At the grounding line, we measure an average speed increase of ~5 m/yr2, with some flow units accelerating by over 11 m/yr2. We find that the spatial pattern of change in ice speed is consistent with the regions of strongest surface lowering, which on some flow units occurs at rates of up to -2.4 m/yr. Our observations show that ice speedup is greatest where the ice is thickest (>700 m), and grounded most deeply. This long 25-year record of change also shows that on some ice streams, the rate of change in ice speed has not been constant throughout the study period. In some regions where ocean temperature measurements are also available, we find that increases in ice speed coincide with the periodic presence of circumpolar deep water, which may therefore be responsible for driving this change. In summary, this study provides a new record of change in ice speed for a rapidly evolving region of Antarctica. In the future, it will be important to use both ocean models and observations to improve our understanding of how ocean forcing is driving dynamic imbalance in the region. This will improve our understanding of the physical mechanisms driving change in Antarctica, helping us to better constrain the ice sheets future contribution to global sea level rise.

How to cite: Selley, H., Hogg, A., Cornford, S., Shepherd, A., Dutrieux, P., Wuite, J., Kusk, A., Nagler, T., and Gilbert, L.: Increased ice flow in the Getz region of West Antarctica, from 1994 to 2018 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15996, https://doi.org/10.5194/egusphere-egu2020-15996, 2020.

EGU2020-15477 | Displays | CR5.7

Basal melting of Dronning Maud Land ice shelves twice as high as previously estimated

Sophie Berger, Veit Helm, Tore Hattermann, Niklas Neckel, Quentin Glaude, Ole Zeising, Sainan Sun, Frank Pattyn, and Olaf Eisen

Basal melting of floating ice shelves is the main process by which  the Antarctic ice sheet is currently losing ice and is responsible for the accelerating Antarctic contribution to sea-level rise. Moreover, basal melting can strongly vary both spatially and temporally. Detailed observations on high  spatio-temporal scales remain however challenging, not to mention accounting for them in ice-sheet models. 

In this study, we combine CryoSat-2 and TanDEM-X elevation changes to capture in unprecedented detail the spatial (and temporal) variability of ice-shelf basal melting in the entire region of Dronning Maud Land, East Antarctica. The high spatial resolution of TanDEM-X elevations provide us with great  details on the spatial variability of the basal mass balance, whereas CryoSat-2 elevations inform us about temporal changes.

We find sub-shelf melt rates that average 1 m/a for the whole of Dronning Maud Land. Those relatively low melt rates conceal however a significant spatial variability on a wide range of scales (from sub-kilometers to ice-shelf wide scales). Spatially integrated, this basal melting represent  an annual basal loss ~140 Gt/a. This revised estimate corresponds to a two-fold increase compared to previous estimates, which could question the relative stability of ice shelves in this region. 

This study highlights different regimes in sub-shelf melting in Dronning Maud Land and  sheds new light on ice-ocean interactions in a region of Antarctica that has long been considered as very stable and which is therfore regularly overlooked.

How to cite: Berger, S., Helm, V., Hattermann, T., Neckel, N., Glaude, Q., Zeising, O., Sun, S., Pattyn, F., and Eisen, O.: Basal melting of Dronning Maud Land ice shelves twice as high as previously estimated , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15477, https://doi.org/10.5194/egusphere-egu2020-15477, 2020.

EGU2020-278 | Displays | CR5.7

A 3-D Model of Antarctic Ice Shelf Surface Hydrology

Sammie Buzzard and Alex Robel

Understanding the surface hydrology of ice shelves is an essential first step to reliably project future sea level rise from ice sheet melt. The formation of surface meltwater has been linked with the disintegration of many ice shelves in the Antarctic Peninsula over the last several decades. The most notable ice shelf collapse occurred in 2002 when significant meltwater lake coverage was observed on the surface of the Larsen B Ice Shelf before its collapse over a period of just a few weeks. Such collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea level rise. Despite the importance of surface meltwater production and transport to ice shelf stability, knowledge of these processes is still lacking and as a result of this, projections of future sea level rise still vary over an order of magnitude.

 

In order to better understand these processes we present a new 3-D model of surface hydrology for Antarctic ice shelves. This model takes the 1-D surface lake formation model of Buzzard et al. (2018) and expands it to three dimensions. It is the first comprehensive model of surface hydrology to be developed for Antarctic ice shelves, enabling us to incorporate key processes such as the lateral transport of surface meltwater. Recent observations suggest that surface hydrology processes on ice shelves are more complex than previously thought, and that processes such as lateral routing of meltwater across ice shelves, ice shelf flexure and surface debris all play a role in the location and influence of meltwater. Our model allows us to account for these as well as additional key physical processes and is calibrated and validated through both remote sensing and field observations.

 

Here we present results of coupling the 1-D model with a 3-D meltwater routing scheme. This includes calculations of the surface energy balance, meltwater production, percolation and refreezing and lake formation. Through case studies, calibrated and validated against observations, we will demonstrate the varied applications of the model.

 

This community-driven, open-access model, has been developed with input from observations, and allows us to provide new insights into surface meltwater distribution on Antarctica’s ice shelves. This enables us to answer key questions about their past and future evolution under changing atmospheric conditions and vulnerability to meltwater driven hydrofracture and collapse.

 

How to cite: Buzzard, S. and Robel, A.: A 3-D Model of Antarctic Ice Shelf Surface Hydrology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-278, https://doi.org/10.5194/egusphere-egu2020-278, 2020.

EGU2020-12645 | Displays | CR5.7

A Mathematical Modeling for Stability of Ice Shelves

Maryam Zarrinderakht and Christian Schoof

Iceberg calving is the reason for more than half of mass loss in both Greenland and Antarctica. It also indirectly contributes to sea-level rise; changes in calving rate can shorten the ice shelves, speed up the grounded ice and increase changes in ice sheets. Therefore, having a better understanding of this phenomenon by a mathematical modeling seems essential.
Lacking of a precise representation of calving in ice sheet and glacier models may yield to nonphysical predictions.
We perform a parameter study to identify groups of key parameters. Here we use boundary element method and compare our result to works done by van der Veen (1998) and Nick et al. (2010). 
 A hydraulic crack propagation is assumed to happen vertically from both base and surface of the shelf. The solution for different scenarios is analysed in the form of stability of a dynamical system. An unstable solution results in an iceberg calving which leads us to a general calving law. 

How to cite: Zarrinderakht, M. and Schoof, C.: A Mathematical Modeling for Stability of Ice Shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12645, https://doi.org/10.5194/egusphere-egu2020-12645, 2020.

EGU2020-8352 | Displays | CR5.7

A simple but robust model for the buttressing of calving glaciers through ice mélange

Tanja Schlemm and Anders Levermann

Under future warming scenarios, both ice sheets on Greenland and Antarctica are likely to discharge ice into the ocean at an accelerating rate. In many regions along the coast of the ice sheets, the icebergs are discharged into a bay. If the addition of icebergs through calving is faster than their transport out of the embayment, the icebergs will be frozen into a mélange with surrounding sea ice. In this case, the buttressing effect of the ice mélange can be considerably stronger than any buttressing by mere sea ice would be. This in turn stabilizes the glacier terminus and leads to a reduction in calving rates. Here we propose a simple but robust buttressing model of ice mélange. 

How to cite: Schlemm, T. and Levermann, A.: A simple but robust model for the buttressing of calving glaciers through ice mélange , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8352, https://doi.org/10.5194/egusphere-egu2020-8352, 2020.

EGU2020-21958 | Displays | CR5.7

A Material Point Method for Glacier Calving

Johan Gaume, Ming Gao, Joshua Wolper, Martin P. Luethi, Andreas Vieli, Joseph Teran, and Chenfanfu Jiang

Glaciers calving ice into the ocean is predicted to significantly contribute to sea-level rise and will thus influence future climate. Although numerous factors that induce glacier calving have been identified and studied, it is still extremely challenging to develop a unified and continuum computational framework that simulates ice fracture and glacier calving taking into account all important ingredients such as the interaction between ice and water, including buoyancy and melting, on complex and large scale geometry. This prevents scientists to precisely predict calving rates at the outlet of glaciers. Here, we propose to address this issue through numerical simulations of glacier calving based on the Material Point Method and finite strain elastoplasticity. A non-associative Cam-Clay model was developed to simulate the ice while the water is modeled as a nearly in-compressible fluid. First, simplified 2D simulations were performed to analyse the size of calved icebergs which were in good agreement with analytical solutions. The model reproduces not only the vertical glacier fracture observed in real calving events but also iceberg formation and tsunami-wave generation. Finally, 3D simulations of glacier calving were performed, taking into account opened crevasses on the top of the glacier. Although at a preliminary stage, and lacking experimental validation, we show the promise of our approach for modeling glacier calving, and more generally glacier and sea-ice dynamics.

How to cite: Gaume, J., Gao, M., Wolper, J., Luethi, M. P., Vieli, A., Teran, J., and Jiang, C.: A Material Point Method for Glacier Calving, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21958, https://doi.org/10.5194/egusphere-egu2020-21958, 2020.

EGU2020-838 | Displays | CR5.7

Geometric Controls of Fjord Glacier Dynamics

Thomas Frank, Henning Åkesson, Basile de Fleurian, and Kerim H Nisancioglu

Retreat of marine outlet glaciers and ice shelves may initiate depletion of inland ice and lead to ice loss that by far exceeds what would be expected from ocean and atmospheric warming alone. Many marine outlet glaciers draining large parts of past and present ice masses have shown non-linear and variable retreat rates, with adjacent glaciers sometimes showing a highly different response to the same large-scale climate forcing. This suggests that individual glacier characteristics play a dominant role in governing retreat.

There is widespread evidence that the dynamic glacier adjustment to an external forcing is highly influenced by fjord topography. However, whether this stabilizes the glacier, or promotes enhanced retreat, depends on the shape of the fjord. So far, no rigorous, systematic assessment of the exact influence of certain geometric features such as overdeepenings or embayments has been undertaken in a model framework that incorporates all relevant processes in a 3D layout.

Here, we analyze a multitude of topographic settings and scenarios using the Ice Sheet System Model (ISSM), which accounts for all relevant physics in a 3D framework. Using artificial fjord geometries, we investigate glacier-topography interaction and quantify the modeled glacier response directly in relation to topographic features.

In light of our modeled topographic influence on glacier retreat, we consider whether we reliably can extrapolate observations from a few well-monitored glaciers to those less studied. Furthermore, we discuss implications for past and future ice sheet mass loss and associated sea-level rise. Finally, a deeper understanding of processes at the glacier front improves confidence in the climate signal derived from the deglacial landscape, as glacier-proximal landforms can more confidently be linked to climate.

How to cite: Frank, T., Åkesson, H., de Fleurian, B., and Nisancioglu, K. H.: Geometric Controls of Fjord Glacier Dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-838, https://doi.org/10.5194/egusphere-egu2020-838, 2020.

The rate of ice flux from the Greenland Ice Sheet to the ocean depends on the ice flow velocity through outlet glaciers. Ice flow velocity, in turn, evolves in response to multiple geographic and environmental forcings at different timescales. For example, velocity may vary daily in response to ocean tides, seasonally in response to surface air temperature, and multi-annually in response to long-term trends in climate. The satellite observations processed as part of the NASA MEaSUREs Greenland Ice Sheet Velocity Map allow us to analyse variations in ice surface velocity at multiple timescales. Here, we decompose short-term and long-term signals in time-dependent velocity fields for Greenland outlet glaciers based on the methods of Riel et al. (2018). Patterns found in short-term signals can constrain basal sliding relations and ice rheology, while the longer-term signals hint at decadal in/stability of outlet glaciers. We present example velocity time series for outlets including Sermeq Kujalleq (Jakobshavn Isbrae) and Helheim Glacier, and we highlight features indicative of dynamic drawdown or advective restabilization. Finally, we comment on the capabilities of a time series analysis software under development for glaciological applications.

How to cite: Ultee, L., Riel, B., and Minchew, B.: Seasonal to multi-annual speedup and slowdown of Greenland outlet glaciers inferred from time-dependent remote sensing observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12679, https://doi.org/10.5194/egusphere-egu2020-12679, 2020.

EGU2020-2433 | Displays | CR5.7

Distributed fibre-optic temperature sensing in a 1 km borehole drilled on a fast-flowing glacier in Greenland

Robert Law, Poul Christoffersen, Bryn Hubbard, Samuel Doyle, Thomas Chudley, Marion Bougamont, and Charlie Schoonman

Whilst marine-terminating glaciers in Greenland are significant contributors to global sea level rise, their thermodynamics are poorly constrained by observations. Conventional discrete thermistor borehole sensing studies go some way to addressing this but lack the spatial resolution to effectively resolve key processes. Here, we detail results from fibre optic distributed temperature sensing equipment installed in a 1040 m hot water drilled borehole 28 km inland of the calving front of Store Glacier, Greenland. Surface ice velocity at the borehole is 550 m a-1 with convergent ice flow into a bedrock trough. Spatial resolution of 0.25 m, temperature differences of 0.03 °C, and an absolute temperature accuracy of 0.15 °C were achieved. 0.5 °C warm anomalies were observed between 0-30 and 220-45 m depth with a central cold section down to -22 °C . We interpret the former anomaly to be a result of cryo-hydrologic warming, although of lower magnitude than in slow-flowing sectors of the Greenland Ice Sheet. The latter is theorised to be strain heating, supported by deformation observed in the cable at this point. The record also reveals a 75 m thick section of temperate basal ice and the nature of the cold-temperate transition as a sharp temperature drop of 0.45 °C over 1.5 m at the top of the temperate layer, with notable temperature changes in the vicinity of the transition. Warming of 0.06 °C is observed over the basal 6 m of the profile. The cable lasted 6 weeks before failure, demonstrating the feasibility of using  fibre optic sensing to study thermal processes in a glacier environment with high deformation rates.

How to cite: Law, R., Christoffersen, P., Hubbard, B., Doyle, S., Chudley, T., Bougamont, M., and Schoonman, C.: Distributed fibre-optic temperature sensing in a 1 km borehole drilled on a fast-flowing glacier in Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2433, https://doi.org/10.5194/egusphere-egu2020-2433, 2020.

EGU2020-14759 | Displays | CR5.7

In-situ basal melt rate distribution of the floating tongue of 79°N Glacier, Greenland

Ole Zeising, Daniel Steinhage, Niklas Neckel, Julia Christmann, Veit Helm, Nils Dörr, and Angelika Humbert

The 79°N Glacier (79NG) in northeast Greenland, one of the last glaciers in Greenland with a floating ice tongue, plays a crucial role for buttressing the North-East Greenland Ice Stream (NEGIS). Remote-sensing studies indicate high basal melt rates (> 50 m/a) near the grounding line but these methods are limited by the hinge zone, where the floating ice is not in hydrostatic equilibrium. As part of the Greenland Ice Sheet Ocean Interaction (GROCE) project, we have performed a dense grid of repeated measurements with a phase-sensitive radio echo sounder (pRES) accompanied with autonomous pRES (ApRES) stations to estimate basal melt rates focusing on the hinge zone of 79NG. For analysing the pRES measurements, we additionally used ice thickness information derived from AWI’s ultra-wideband radar (UWB) revealing steep channels at the base. The estimated basal melt rates downstream the hinge zone are approximately the same as satellite-derived melt rates. In the hinge zone we found by far larger basal melt rates exceeding 100 m/a next to basal channels.

How to cite: Zeising, O., Steinhage, D., Neckel, N., Christmann, J., Helm, V., Dörr, N., and Humbert, A.: In-situ basal melt rate distribution of the floating tongue of 79°N Glacier, Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14759, https://doi.org/10.5194/egusphere-egu2020-14759, 2020.

EGU2020-9749 | Displays | CR5.7

Glacier-plume or glacier-fjord circulation models? A model intercomparison for Hansbreen-Hansbukta system, Svalbard

Eva De Andrés, Jaime Otero, and Francisco Navarro

Up to 30% of the global tidewater mass loss corresponds to frontal ablation through submarine melting and calving. However, the glacier-fjord interactions remain poorly understood and challenging to constrain in the models. We have developed a 2D glacier flowline-plume coupled model that includes subglacial discharge, submarine melting and iceberg calving to simulate Hansbreen-Hansbukta system (SW Svalbard). We run the model for 20 weeks, from April to September of 2010, with weekly information exchange between glacier and plume models. The same set up and constraints of a previous glacier-fjord circulation model are used here, making the results of both simulations comparable. We consider a 200 m-width subglacial discharging channel, which was found to be a good approximation in the previous glacier-fjord model. Submarine melt rates show high sensitivity to the subglacial-discharge and ambient fjord-temperature intraseasonal evolution. Calving rates are highly dependent on both submarine melting and crevasse water depth. Glacier-plume and glacier-fjord coupled models differ in vertically-accumulated submarine melt rates (up to 30 % higher for the glacier-plume model) and show different melt-undercutting front shapes, which have an influence on the net stress fields near the glacier front. The quasi-linear melt-undercutting morphology exhibited by the glacier-plume model promotes higher calving rates than the quasi-parabolic front shape resulting from the glacier-fjord model, although both models predict similar front positions. Given that the glacier-plume model diminishes the computational cost by a factor of >50, we think that it is a good option for projection studies, as long as we apply appropriate constraints to subglacial discharge fluxes and ambient fjord temperatures.

How to cite: De Andrés, E., Otero, J., and Navarro, F.: Glacier-plume or glacier-fjord circulation models? A model intercomparison for Hansbreen-Hansbukta system, Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9749, https://doi.org/10.5194/egusphere-egu2020-9749, 2020.

EGU2020-2771 | Displays | CR5.7

Dynamics of a subglacial meltwater plume revealed by continuous subsurface monitoring directly on the calving front

Evgeny A. Podolskiy, Naoya Kanna, and Shin Sugiyama

Recent literature has highlighted the great importance of subglacial meltwater plumes in a variety of processes including subaqueous ice melting, enhanced fjord-scale circulation, nutrient and heat mixing, foraging ground formation, and the movements of seals that apparently use plumes for returning to the sea surface.

However, direct measurements of plume water properties are scarce due to the difficulty of conducting observations near unstable glacier calving fronts. A few studies have succeeded in obtaining snapshot views of plume structures using bio-logging, remotely operated vessels, or helicopter-borne eXpendable Conductivity Temperature Depth (XCTD) probes, but continuous data time-series remain elusive and technically challenging.

In this study, we overcame these limitations by deploying mooring-based equipment between major calving events from a calving front of Bowdoin Glacier, an ocean-terminating glacier in Northwest Greenland. In July 2017, a first-of-its-kind 10 d dataset of plume dynamics was obtained by attaching instruments to the ice cliff for the logging of conductivity, temperature, and pressure at depths of ~5 m and ~100 m, with a sampling interval of 10 s.

Nonlinear and spectral time-series analysis revealed a chaotic system, an extremely turbulent environment, the presence of coherent structures, tide-modulated signals, and a non-intuitive transition in the dynamics of the plume due to a witnessed glacial lake outburst flood. Our observations should provide an important reference for the glacier-science community, including modellers interested in the evolution of ocean-terminating glaciers, fjord-scale circulation, and glacier fjord ecosystems.

How to cite: Podolskiy, E. A., Kanna, N., and Sugiyama, S.: Dynamics of a subglacial meltwater plume revealed by continuous subsurface monitoring directly on the calving front, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2771, https://doi.org/10.5194/egusphere-egu2020-2771, 2020.

Freshwater export from the Greenland Ice Sheet to the surrounding ocean has increased by 50% since the early 1990s, and may triple over the coming century under high greenhouse gas emissions. This increasing freshwater has the potential to influence both the regional and large-scale ocean, including marine ecosystems. Yet quantification of these impacts remains uncertain in part due to poor characterization of freshwater export, and in particular the transformation of freshwater around the ice sheet margin by ice-ocean processes, such as submarine melting, plumes and fjord circulation. Here, we combine in-situ observations, ocean reanalyses and simple models for ice-ocean processes to estimate the depth and properties of freshwater export around the full Greenland ice sheet from 1991 to present. The results show significant regional variability driven primarily by the depth at which freshwater runoff leaves the ice sheet. Areas with deeply-grounded marine-terminating glaciers are likely to export freshwater to the ocean as a dilute mixture of freshwater and externally-sourced deep water masses, while freshwater from areas with many land-terminating glaciers is exported as a more concentrated mixture of freshwater and near-surface waters. A handful of large glacier-fjord systems dominate ice sheet freshwater export, and the vast majority of freshwater export occurs subsurface. Our results provide an ice sheet-wide first-order characterization of how ice-ocean processes modulate Greenland freshwater export, and are an important step towards accurate representation of Greenland freshwater in large-scale ocean models.

How to cite: Slater, D. and Straneo, F.: Depth and properties of freshwater export from the Greenland Ice Sheet modulated by ice-ocean processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12976, https://doi.org/10.5194/egusphere-egu2020-12976, 2020.

EGU2020-3261 | Displays | CR5.7

A look beneath the ice shelves of western Dronning Maud Land, East Antarctica: subglacial topography linked to ice shelf stability

Hannes Eisermann, Graeme Eagles, Antonia Ruppel, Emma C. Smith, and Wilfried Jokat

Antarctica’s ice shelves play a key role in stabilizing their related ice sheets. The ice shelves of western Dronning Maud Land – including the Ekström, Atka, Jelbart, Fimbul and Vigrid ice shelves – currently buttress a catchment that comprises an ice volume equivalent to 0.95 meters of sea level. Any future increase in ice shelf mass loss, with basal melting likely being the main cause, will inevitably accelerate ice sheet drainage and contribute to global sea level rise. Since basal melting largely depends on ice-ocean interactions, it is crucial to attain reliable and consistent bathymetry models to estimate water and heat exchange beneath these ice shelves. We have constructed bathymetry models for an area of about 63,000 km2 beneath the ice shelves of western Dronning Maud Land by inverting airborne gravity data, tied to radar, seismic, and offshore depth reference points. New high-resolution airborne magnetic data across the ice shelves point to Jurassic intrusions and seaward-dipping reflectors originating from Gondwana breakup; enabling us to consider geological density variations as part of the bathymetry modelling process. Our bathymetric models reveal deep glacial troughs beneath the ice shelves, and sills close to the continental shelf breaks which currently limit the possible entry of Warm Deep Water from the Southern Ocean. The present-day average thermocline depth is comparable to the average depths of saddles along the sills, which present gateways into the sub-ice cavities. This leads us to suggest a high sensitivity for these ice shelves to changes in ocean temperature and especially thermocline depth in the future. Once a significant amount of warm water overtops the sills, the deep troughs will allow for fast access to the grounding line, after which it seems there may be little to stop basal melting from rapidly eroding the ice shelves of western Dronning Maud Land.

How to cite: Eisermann, H., Eagles, G., Ruppel, A., Smith, E. C., and Jokat, W.: A look beneath the ice shelves of western Dronning Maud Land, East Antarctica: subglacial topography linked to ice shelf stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3261, https://doi.org/10.5194/egusphere-egu2020-3261, 2020.

EGU2020-18566 | Displays | CR5.7

Amery Ice Shelf Grounding line detection using Cryosat-2 and Landsat8 data fusion

Yu Zhang, Tingting Zhu, Shengkai Zhang, and Fei Li

We propose a grounding line detection algorithm for Amery Ice Shelf (AIS) using Cryosat-2 altimetry and Landsat8 optical data. The Grounding line represents the area where ice sheet separates from Antarctic ice cap and extends into the ocean, which is the key indicator of the inland ice sheet instability and the boundary conditions of numerical model for ice velocity calculation. Many studies focus on grounding line retrieval using altimetry data or remote sensing data either with lower spatial resolution or discontinuous, which makes it difficult for large scale and long-terms analysis. In this abstract, Bayesian MAP (Maximum a posteriori probability criterion) based Cryosat-2 altimetry and Landsat8 optical data fusion algorithm is proposed for grounding line extraction in AIS, Antarctic. For Cryosat-2 data, the along track based slope analysis is used to calculate the Gaussian curvature and mean curvature, where the area with largest slope variance is defined as the grounding points, which will act as the control points in the fusion framework. For the Landsat8 imagery with the spatial resolution of 30m, we first generate the 1km grid using cubic Hermite method. Based on the similarity measurement between texture feature and grounding line area, where the area with largest variance of mean value and standard deviation is defined as the grounding line in Landsat8 data.  For the MAP based fusion grounding line extraction step, the optimal procedure is to find the minimum distance between the Cryosat-2 grounding points and Landsat8 grounding line within a given area, so as to maintain the smoothness and discontinuous where the optical data is missing or the texture feature is not obvious. In the experiment part, the proposed result is compared with MODIS grounding line products, and the results indicate that the mean value is similar with Landsat8 result and standard deviation is lower. Moreover, since the Cryosat-2 data is not obstacle by cloud, it can provide continuous observation for AIS grounding line. Besides, the time series analysis shows that from 2016-2018, the grounding line did not change so much, which means that the AIS is stable with lower expansion rate.   

How to cite: Zhang, Y., Zhu, T., Zhang, S., and Li, F.: Amery Ice Shelf Grounding line detection using Cryosat-2 and Landsat8 data fusion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18566, https://doi.org/10.5194/egusphere-egu2020-18566, 2020.

EGU2020-6108 | Displays | CR5.7

Intermittent freeze-melt pattern detected at the base of the Ronne Ice Shelf

Irena Vankova and Keith Nicholls

High salinity shelf water (HSSW) is a water mass that drives melting at the Ronne Ice Shelf, entering the sub ice shelf cavity at the western end of the ice front. To monitor the rate of ice shelf basal melting along the path of assumed HSSW inflow, a phase-sensitive radar (ApRES) was deployed and it sampled autonomously for over two years. Although the site is found to melt on average, the data show evidence of freezing occurring intermittently throughout the observed time period. Here we systematically investigate oceanographic processes that could give rise to these observations. Further, we address the question of whether ApRES can be used to quantify the rate of basal freezing.

How to cite: Vankova, I. and Nicholls, K.: Intermittent freeze-melt pattern detected at the base of the Ronne Ice Shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6108, https://doi.org/10.5194/egusphere-egu2020-6108, 2020.

EGU2020-13277 | Displays | CR5.7

Channelized Antarctic ice shelf melting from high-resolution remote sensing

Stef Lhermitte, Jeffrey Nederend, and Bert Wouters

Antarctic mass loss is the largest source of uncertainty in current sea level rise projections. Ice shelf instability plays a key role in this uncertainty as ice shelves are the floating gatekeepers that surround 75% of Antarctica’s coastline and that buttress the contribution of grounded ice to sea level rise. Although basal melting has been identified as one of the key processes for ice shelf instability, the quantitative understanding of this process and how much, how fast it weakens ice shelves is limited as it is determined by fine scale processes (e.g. channelized basal melting) that until recently were difficult to quantify. The recent availability of high-resolution, multi-source satellite imagery (e.g. stereoscopic DEMs from the Reference Elevation Model of Antarctica (REMA) or swath-processing of Cryosat-2), however, offers the opportunity to quantify the role of channelized melting on ice shelf instability across Antarctica.

In this study, we use REMA, Cryosat-2 and IceBridge elevation data to develop high-resolution indicators of basal melt across some major Antarctic ice shelves (Dotson, Pine Island, Larsen C). The methodology consists of processing time series of high-resolution REMA strips in a Lagrangian framework while accounting for tilt and tide corrections.

Comparison of different approaches (e.g. simplified REMA-only approach; combined REMA-Cryosat-2 approach, combined REMA-IceBridge approach) shows that the simplified approach can be applied easily to develop Antarctic wide estimates of basal melting across Antarctica, while the combined REMA-Cryosat-2 shows the highest accuracy. Results of this study, finally, show the potential of using REMA for developing high resolution basal melt products across Antarctica and providing insight in the spatial variability of basal melting due to channelized melting.

How to cite: Lhermitte, S., Nederend, J., and Wouters, B.: Channelized Antarctic ice shelf melting from high-resolution remote sensing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13277, https://doi.org/10.5194/egusphere-egu2020-13277, 2020.

EGU2020-22338 | Displays | CR5.7

Instabilities in extensional flows and the dynamics of rifts in ice-shelves

Lielle Stern and Roiy Sayag

Ice shelves that spread into the ocean can develop rifts, which can trigger ice-berg calving and enhance ocean-induced melting. Fluid mechanically, this system is analogues to the propagation of a non-Newtonian, strain-rate-softening fluid representing ice that displaces a relatively inviscid and denser fluid that represents an ocean. Recent scaled laboratory experiments have shown that when the flow geometry is circular the front of the displacing non-Newtonian fluid, which represents the leading edge of a shelf, can become unstable and evolve finger-like patterns comprised of rifts and tongues (Sayag & Worster, 2019a). As the rifts and tongues evolved, their number declined with time through the closure of some rifts.

In this study we focus on the weakly nonlinear stability of the propagating front. We consider an annular ice shelf having a fixed grounding line and an edge that evolves due to constant mass flux across the grounding line. We investigate the time evolution of the perturbed front to quantify the instability mechanism and the reduction of the number of rifts and tongues over time. The model predictions have better agreement with experimental measurements than previous studies. Our analysis elucidates the formation and evolution of rifts in ice shelves and provides testable predictions.

How to cite: Stern, L. and Sayag, R.: Instabilities in extensional flows and the dynamics of rifts in ice-shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22338, https://doi.org/10.5194/egusphere-egu2020-22338, 2020.

The propagation of high-frequency elastic-flexural waves through an ice shelf was modeled by a full 3-D elastic model, which also takes into account sub-ice seawater flow. The sea water flow is described by the wave equation. Numerical experiments were undertaken both for an intact ice shelf free of crevasses, which has idealized rectangular geometry, and for a crevasse-ridden ice shelf. The crevasses were modeled as triangle/rectangular notches into the ice shelf. The obtained dispersion spectra (the dispersion curves describing the wavenumber/periodicity relation) are not continuous. The spectra reveal gaps that provide the transition from n-th mode to (n+1)-th mode. These gaps are observed both for an intact ice shelf free of crevasses and for a crevasse-ridden ice shelf. They are aligned with the minimums in the amplitude spectrum. That is the ice shelf essentially blocks the impact wave at this transition. However, the dispersion spectrum obtained for a crevasse-ridden ice shelf, has a qualitatively difference from that obtained for an intact ice shelf free of crevasses. Moreover, the dispersion spectrum obtained for a crevasse-ridden ice shelf reveals the band gap – the zone there no eigenmodes exist (Freed-Brown and others, 2012). The numerical experiments with the crevasse-ridden ice tongue that is 16 km in longitudinal extent, 0.8km width and 100m thick, were undertaken for a wide range of the periodicities of the incident wave: from 5 s to 250 s. The obtained dispersion spectra reveal two band gaps in this range: the first band gap at about 20 s and the second band gap at about 7 s for 1km spatial periodicity of the crevasses. The width of the band gap significantly increases when the crevasses depth increases too. Respectively, the amplitude spectra reveal significantly increasing area of periodicities/frequencies where the ice shelf blocks the impact wave.

References

Freed-Brown, J., Amundson, J., MacAyeal, D., & Zhang, W. (2012). Blocking a wave: Frequency band gaps in ice shelves with periodic crevasses. Annals of Glaciology, 53(60), 85-89. doi:10.3189/2012AoG60A120

Konovalov, Y.V. (2019). Ice-shelf vibrations modeled by a full 3-D elastic model. Annals of Glaciology, 1-7. doi:10.1017/aog.2019.9

How to cite: Konovalov, Y.: The effect of the blocking of impact ocean waves by the crevasse-ridden ice shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9665, https://doi.org/10.5194/egusphere-egu2020-9665, 2020.

EGU2020-19856 | Displays | CR5.7

Ice front blocking of ocean heat transport to an Antarctic ice shelf

Anna Wåhlin, Nadine Steiger, Elin Darelius, Karen Assmann, Mirjam Glessmer, Ho Kyung Ha, Laura Herraiz-Borreguero, Celine Heuzé, Adrian Jenkins, Tae Wan Kim, Aleksandra Mazur, Joel Sommeria, and Samuel Viboud

Shoreward oceanic heat flux in deep channels on the continental shelf typically far exceeds that required to match observed ice shelf melt rates, suggesting other critical controls.  IN the present study we study the depth-independent (barotropic) and the density-driven (baroclinic) components of the flow of warm ocean water towards an ice shelf. Using observations from the Getz Ice Shelf system as well as geophysical laboratory experiments on a rotating platform, it is shown that the dramatic step shape of the ice front blocks the barotropic component, and that only the baroclinic component, typically much smaller, can enter the sub-ice cavity.  A similar blocking of the barotropic component may occur in other areas with comparable ice-bathymetry configurations, which may explain why changes in the density structure of the water column have been found to be a better indicator of basal melt rate variability than the heat transported onto the continental shelf. Representing the step topography of the ice front accurately in models is thus important for simulating the ocean heat fluxes and induced melt rates.

How to cite: Wåhlin, A., Steiger, N., Darelius, E., Assmann, K., Glessmer, M., Ha, H. K., Herraiz-Borreguero, L., Heuzé, C., Jenkins, A., Kim, T. W., Mazur, A., Sommeria, J., and Viboud, S.: Ice front blocking of ocean heat transport to an Antarctic ice shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19856, https://doi.org/10.5194/egusphere-egu2020-19856, 2020.

EGU2020-18743 | Displays | CR5.7

Coupled ocean—ice shelf—ice sheet projections for the Weddell Sea Basin, Antarctica

Ralph Timmermann and Torsten Albrecht

To study Antarctica’s contribution to ongoing and future sea level rise, a coupled ice sheet – ice shelf – ocean model with an explicit representation of ice shelf cavities has been developed. The coupled model is based on a global implementation of the Finite Element Sea ice Ocean Model (FESOM) with a mesh that is substantially refined in the marginal seas of the Southern Ocean. The Antarctic Ice Sheet is represented by a regional setup of the Parallel Ice Sheet Model PISM, comprising the Filchner-Ronne Ice Shelf (FRIS) and the grounded ice in its catchment area up to the ice divides.  At the base of the FRIS, melt rates and ocean temperatures from FESOM are applied. PISM returns ice thickness and the position of the grounding line. Buildung on infrastructure developed for the Regional Antarctic and Global Ocean (RAnGO) model, we use a pre-computed FESOM mesh that is adopted to the varying cavity geometry in each coupling step, i.e. currently once per model year. Changes in water column thickness are easily accounted for by the terrain-following vertical coordinate system in the ice shelf cavity. The ice sheet model is run on a horizontal grid with 1 km resolution to ensure an appropriate representation of grounding line processes. Enhancement factors for the approximation of the stress balance, as often used in coarse-resolution ice sheet models, become obsolete at such high resolution. Ice stream flow is well captured by polythermal coupling of the ice flow and a Mohr-Coulomb yield stress criterion that accounts for properties of the till material and the effective pressure on the saturated till. We present results from model runs with a 20th-century climate forcing and projections until the end of the 22nd century. We will show that cavity hydrography, ice shelf basal melt rates and thickness evolution as well as the feedback on grounded ice  in the coupled model simulations are very sensitive to the atmospheric forcing scenario applied.

 

 

How to cite: Timmermann, R. and Albrecht, T.: Coupled ocean—ice shelf—ice sheet projections for the Weddell Sea Basin, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18743, https://doi.org/10.5194/egusphere-egu2020-18743, 2020.

EGU2020-12987 | Displays | CR5.7

Exploring and reducing biases in sub-ice-shelf melt rates in an Earth system model

Xylar Asay-Davis, Carolyn Begeman, Darin Comeau, Matthew Hoffman, Wuyin Lin, Mark Petersen, Stephen Price, Andrew Roberts, Milena Veneziani, and Jonathan Wolfe

Sub-ice-shelf melting plays a critical role in the dynamics of the Antarctic Ice  Sheet and also feeds back on the regional climate, transforming ocean properties (e.g., affecting deep-water production and sea-ice formation).  A full understanding of these processes, as well as the ability to project their response to a changing climate, requires Earth System Models (ESMs) that include coupling with ice-sheet processes.  However, biases in regional Antarctic climate can be amplified through sub-ice-shelf melting, and biased melt rates can have significant adverse effects on ice-sheet model initialization and evolution.  In preparation for inclusion of dynamic ice sheets in ESMs, this presentation discusses our recent experience in understanding the causes of biases in ocean properties on the Antarctic continental shelf and their relationship to ice-shelf melting.  Differences in model behavior across configurations and simulations using the Energy Exascale Earth System Model (E3SM) demonstrates a sensitivity of melt rates to climate. We assess the sensitivity of those melt rates to changes in the region’s climate, including freshening on the continental shelf and shoaling of the thermocline. We also show that ice-shelf meltwater feeds back onto the climate, for example, by affecting melting under neighboring ice shelves, sometimes dramatically so.  We demonstrate that significant reductions in melt-rate biases can be achieved through modifications to ocean model mixing parameterizations. This work charts a path forward for configuring ESMs to produce realistic Antarctic melt rates.

How to cite: Asay-Davis, X., Begeman, C., Comeau, D., Hoffman, M., Lin, W., Petersen, M., Price, S., Roberts, A., Veneziani, M., and Wolfe, J.: Exploring and reducing biases in sub-ice-shelf melt rates in an Earth system model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12987, https://doi.org/10.5194/egusphere-egu2020-12987, 2020.

EGU2020-11279 | Displays | CR5.7

Towards tackling ice-sheet ocean interaction with Finite Element Methods

Stefano Ottolenghi and Josefin Ahlkrona

Ice sheet-ocean interaction is important to properly understand phenomena such as ice sheet melting and ocean circulation. While the long term goal of this project is to fully couple the ice and ocean in one single numerical framework, we here start by modelling the ocean. We use the full non-hydrostatic equations in order to accurately model the complex ocean dynamics near the ice sheets. As numerical method, we employ finite element methods due to their capability of representing a complex fjord geometry and locally refining the mesh in the areas which require more careful handling, and its strong mathematical foundation. This will allow to overcome classical problems such as representing a moving ice shelf in a discretized setting. We here present an example of modeled fjord circulation obtained simulating the model with the FEniCS computing platform.

How to cite: Ottolenghi, S. and Ahlkrona, J.: Towards tackling ice-sheet ocean interaction with Finite Element Methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11279, https://doi.org/10.5194/egusphere-egu2020-11279, 2020.

EGU2020-9101 | Displays | CR5.7

Parameterizing heat and freshwater exchanges driven by subglacial discharge in Greenland's proglacial fjords

Adam Stanway, Andrew Wells, Helen Johnson, and Jeff Ridley

Freshwater flux from the melting of Greenland’s Ice Sheet is thought to account for 25% of the observed rise in global mean sea level between 1992 and 2011, with a significant proportion of this associated with increased freshwater flux from marine terminating glaciers within coastal fjords. It has been suggested that increased ocean temperatures have triggered the retreat of Greenland’s outlet glaciers, with the melting of submarine glacier termini leading to an acceleration of inland regions of the ice sheet. Global climate  models  currently  operate  at  resolutions  too  coarse  to resolve  ice-ocean  interaction  on  the length  scales  typical  of  coastal  fjords. Therefore, a parameterization scheme is required to incorporate the relevant physics into such models.

As a first step towards such a parameterisation scheme, we develop theoretical understanding of the first order controls on heat and freshwater exchanges in Greenland’s proglacial fjords, guided by computational simulations in MITgcm. Fjords are modelled with idealised geometries, considering cases with and without bathymetric sills. The model parameterises melting at the glacier terminus, and non-hydrostatic flow in one or more buoyant plumes that form from fresh subglacial discharge at the glacier grounding line. We systematically explore how the overturning circulation and heat transport through a fjord respond to varying subglacial discharge.

In a subglacial-discharge dominated regime with flat bathymetry, we find that the horizontally integrated vertical flow structure set by buoyant plumes at the ice face remains unmodified along the length of the fjord, and is independent of the fjord width. For cases with either single or multiple subglacial-discharge plumes, we derive scaling laws for the heat and freshwater exchanges using buoyant plume theory, finding that the water in contact with the ice face mirrors that outside the fjord. This picture is complicated in the presence of a bathymetric sill, which can inhibit the transportation of deep coastal waters into the fjord. We conclude by discussing how our scaling laws might be used as a simple parameterisation of proglacial fjord dynamics in regimes where subglacial discharge controls the flow strength. We discuss how these results might be extended to incorporate the competing effects of circulation driven by along-fjord and along-shelf winds.

How to cite: Stanway, A., Wells, A., Johnson, H., and Ridley, J.: Parameterizing heat and freshwater exchanges driven by subglacial discharge in Greenland's proglacial fjords, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9101, https://doi.org/10.5194/egusphere-egu2020-9101, 2020.

EGU2020-8663 | Displays | CR5.7

Modelling the impact of iceberg melt on glacier-ocean interaction, east Greenland

Ben Davison, Tom Cowton, Finlo Cottier, and Andrew Sole

The melting of icebergs within Greenland’s iceberg-choked fjords provides a large and distributed source of liquid freshwater throughout the year. However, the impact of this freshwater flux on fjord properties and circulation remains unclear, in part because icebergs have typically been neglected in modelling studies that seek to examine interaction between glacier and fjord processes. Here, we modify a general circulation model to simulate the impact of iceberg submarine melting within Kangerdlugssuaq and Sermilik fjords in east Greenland, home to two of Greenland’s largest glaciers. We find that iceberg submarine melting results in cooling of up to 5°C and freshening of up to 0.6 psu throughout the upper 100-200 metres of both fjords, compared to experiments without icebergs. The resulting freshwater flux, which is of the order of hundreds of cumecs, is capable of driving a weak overturning circulation. This augments the runoff-driven circulation at depth but can oppose the up-fjord flow of warm near-surface waters, resulting in an increase in up-fjord heat flux at depth but a decrease near the surface. By increasing subsurface iceberg melt rates, ocean warming will therefore expedite iceberg deterioration within ice mélange and may further increase ocean thermal forcing of tidewater glacier grounding lines. Our results highlight the significant impact that icebergs have on fjord water properties and circulation in Greenland’s iceberg-choked fjords, demonstrating the importance of including these processes in studies that seek to examine interactions between the ice sheet and the ocean.

How to cite: Davison, B., Cowton, T., Cottier, F., and Sole, A.: Modelling the impact of iceberg melt on glacier-ocean interaction, east Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8663, https://doi.org/10.5194/egusphere-egu2020-8663, 2020.

EGU2020-8110 | Displays | CR5.7

GPS measurements during two major calving events at Bowdoin Glacier, Greenland

Eef van Dongen, Guillaume Jouvet, Fabian Lindner, Andreas Bauder, Fabian Walter, and Shin Sugiyama

Future mass loss predictions, and thereby sea level rise predictions, are strongly affected by the representation of iceberg calving in numerical ice sheet models. Despite recent advances, gaps in our understanding of calving mechanisms remain and there exists a lack of data to constrain mechanical properties related to ice fracturing. For instance, observed critical strain rates for crevasse initiation span two orders of magnitude.

Bowdoin Glacier in Northwest Greenland provides a unique opportunity to conduct in-situ measurements near the calving front due to its accessibility via a crevasse-free walkable moraine. In July 2019, two major calving events were surveyed by 10 GPS stations installed along the front in close vicinity to the calving events. Measurements show glacier uplift prior to the first calving event and horizontal compression prior to the second major calving event.

In contrast to previously observed major events, no precursor such as a large surface crack was visible on the field. Our data suggest a change in calving behaviour from surface crevasses due to hydro-fracturing to basal crevasse formation due to buoyancy, which may be favoured by observed thinning (~4 m yr-1 since 2013).

How to cite: van Dongen, E., Jouvet, G., Lindner, F., Bauder, A., Walter, F., and Sugiyama, S.: GPS measurements during two major calving events at Bowdoin Glacier, Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8110, https://doi.org/10.5194/egusphere-egu2020-8110, 2020.

EGU2020-14461 | Displays | CR5.7

Ice-shelf and glacier changes in Northern Greenland

Jeremie Mouginot, Eric Rignot, Bernd Scheuchl, Romain Millan, Anders Bjørk, Shivani Ehrenfeucht, and Anna Derkacheva

In the northern sectors of Greenland, that hold more than 2.7 m of sea level equivalent, ice drains through ice shelves similarly to Antarctica. Zachariae Isstrøm, in northeast Greenland, is retreating and accelerating, most probably because of enhanced melting at its ice-shelf bottom followed by its break- up. Nioghalvfjerdsfjorden, its neighbor, is also showing signs of thinning close to its grounding line, as is Petermann Gletscher, located 800_km more to the west. Here, we investigate dynamic and geometrical changes of all current and former ice shelves located along the northern coast of Greenland, namely Humboldt Gletscher, Steensby Gletscher, Ryder Gletscher, Ostenfeld Gletscher, Marie Sophie Gletscher, Academy Gletscher and Hagen Bræ. Using satellite and airborne-based remote- sensing sensors, we reconstruct the time series of speed, grounding-line position, submarine melt, ice thickness and surface elevation changes since the 80s. We will provide an update of the glacier ice discharges and will discuss any large-scale pattern of enhanced melting of the northern Greenlandic ice shelves . We will conclude with the possibility of actual or future destabilization -or lack thereof- of the glaciers in this sector of Greenland.

How to cite: Mouginot, J., Rignot, E., Scheuchl, B., Millan, R., Bjørk, A., Ehrenfeucht, S., and Derkacheva, A.: Ice-shelf and glacier changes in Northern Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14461, https://doi.org/10.5194/egusphere-egu2020-14461, 2020.

EGU2020-16531 | Displays | CR5.7

Investigating calving front morphology as a precursor to dynamic behaviour at a large Greenlandic tidewater glacier

Charlie Bunce, Pete Nienow, Noel Gourmelen, and Tom Cowton

Successful prediction of the response of the Greenland Ice Sheet to climate warming requires accurate estimation of future ice loss from tidewater glaciers. Patterns of tidewater glacier retreat and advance have acted as an important proxy for understanding the processes associated with frontal ablation. It has not however been possible to effectively constrain commonality in these observed patterns that can then be directly linked to the influence of specific controls on ice loss. Here, we investigate planform changes in calving front morphology, an aspect of glacier dynamics that has received little prior attention; however, an improved understanding and quantification of the role of morphometric change in influencing glacier dynamics and iceberg calving may provide critical insights into tidewater glacier behaviour. We develop a buffer analysis method to quantify changes in calving front morphology at Narsap Sermia, a large tidewater glacier in southwest Greenland that has experienced substantial recent retreat. Our results reveal no distinct temporal or spatial patterns in the timing or magnitude of morphological change. Furthermore, we found no statistically significant relationships between morphological change and a range of forcing factors including air temperatures, modelled estimates of subglacial discharge and variations in glacier bed geometry. Our results therefore suggest that process driven morphological terminus change is not an effective predictor of terminus retreat and instead support the application of generalised parameterisations of tidewater glacier retreat within ice-dynamic models.

How to cite: Bunce, C., Nienow, P., Gourmelen, N., and Cowton, T.: Investigating calving front morphology as a precursor to dynamic behaviour at a large Greenlandic tidewater glacier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16531, https://doi.org/10.5194/egusphere-egu2020-16531, 2020.

EGU2020-18633 | Displays | CR5.7

Multi-year observations of calving and front characteristics of two marine terminating outlet glaciers

Andrea Walter, Martin P. Lüthi, Martin Funk, and Andreas Vieli

We observed two outlet glaciers in West- and Nordwest-Greenland with a terrestrial radar interferometer (TRI), pressure sensors and time-lapse cameras over six and two years, respectively. The resulting detailed dataset provides us with insights on the calving process and the changes in front geometry over the last years. Since the two glaciers are characterised by different geometries and velocity fields, the influence of those parameters on the calving process can be investigated. The combination of the three different observation methods enable us to overcome their individual disadvantages. With the time-lapse camera taking pictures of the glacier front every 10 seconds, we detect all calving events of different sizes and styles but cannot quantify the volume. We used the TRI to quantify the volumes of aerial calving events by DEM differentiation. Further, calving waves measured with pressure sensors are used to distinguish between different calving types. We develop a relationship between calving volumes and wave heights and use this as an additional indirect method to estimate calving volumes. We find that the calving style and size as well as the front geometry is mainly controlled by the bed topography and the presence of a subglacial discharge plume. The location of the plume is observed to migrate from year to year, which leads also to changes in the calving pattern. Calving style and pattern as well as glacier velocity fields and geometry changes are additionally compared with environmental conditions such as the air temperature and the presence of ice-mélange in the proglacial fjord. In years with an early spring we find different front characteristics and calving patterns than for years with colder conditions.

How to cite: Walter, A., Lüthi, M. P., Funk, M., and Vieli, A.: Multi-year observations of calving and front characteristics of two marine terminating outlet glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18633, https://doi.org/10.5194/egusphere-egu2020-18633, 2020.

EGU2020-16736 | Displays | CR5.7

Viscoelastic modeling results of the 79°N Glacier, Greenland

Julia Christmann, Martin Rückamp, Ole Zeising, Daniel Steinhage, Niklas Neckel, Veit Helm, Müller Ralf, Mirko Scheinert, Shfaqat Abbas Khan, and Angelika Humbert

Grounding line/zone dynamics of floating-tongue glaciers is of major importance for changes in their contribution to sea-level rise. For floating-tongue glaciers, thermal forcing of oceanic heat and tidal forcing are the major processes acting in that zone. Here we deal with the response to tidal forcing. The 79°N Glacier, an outlet glacier of the North East Greenland Ice Stream, is the focus of the Greenland Ice Sheet Ocean Interaction project (GROCE) funded by the German Ministry of Education and Research. We present a study of this region considering the deformation of the glacier in response to ocean tidal forcing by means of observations and modeling. GPS measurements realized in 2017-2018 are analyzed for vertical and horizontal displacements of the glacier and its floating tongue. Observations on fully-grounded ice reveal a periodic horizontal displacement in response to ocean tidal forcing in a distance of more than 35 km upstream from the grounding line. In the hinge zone, i.e. the transition between grounded and floating ice, the tidal forcing leads to a measurable vertical bending of the ice and a periodic movement of the grounding line. Understanding the mechanisms of grounding line migration is important to better evaluate the contribution of grounded ice discharge to sea-level rise.

In order to model the measured displacements, a viscoelastic material model is required using the observed vertical displacements at the floating ice tongue as external forcing. Geometries obtained from AWI’s new ultrawideband radar form the basis for finite-element simulations in COMSOL. With the viscoelastic Maxwell material model, the response of the ice to ocean tidal forcing can successfully be modeled. Results obtained with a nonlinear Glen-type viscosity agree very well with the observed bending near the grounding line. The expected phase shift of the horizontal displacements upstream from the grounding line is well reproduced in the model.

How to cite: Christmann, J., Rückamp, M., Zeising, O., Steinhage, D., Neckel, N., Helm, V., Ralf, M., Scheinert, M., Khan, S. A., and Humbert, A.: Viscoelastic modeling results of the 79°N Glacier, Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16736, https://doi.org/10.5194/egusphere-egu2020-16736, 2020.

EGU2020-21999 | Displays | CR5.7

Modelling Jakobshavn Isbrae from 2009 to 2018

Matt Trevers, Tony Payne, Steph Cornford, and Anna Hogg

Jakobshavn Isbrae has dramatically accelerated, thinned and retreated since the late 1990s in several stages of retreat and stagnation. Studies have indicated that the loss of buttressing due to retreat of the calving front following the disintegration of its floating ice tongue was the trigger of acceleration and thinning of the terminus, however uncertainty remains over the mechanisms controlling the timing and magnitude of the retreat.

The maximum retreat of the calving front was reached between 2013 and 2015 following the peaking of ice flow speeds in excess of 18 km yr-1. Since 2016, ice flow speeds have decelerated from this peak and the terminus has experienced a modest readvance and thickening. We calculated a calving rate for the period 2009 to 2018 which shows that terminus flow speeds and calving are closely related. Until 2009 a transient loosely bonded ice tongue formed but this feature appears not to have formed from 2010 onwards.

We aim to demonstrate that the signal of thinning and retreat can be reproduced by driving the glacier with the calculated calving rate. We used the BISICLES ice sheet model to simulate the evolution of Jakobshavn Isbrae over the past decade, with the calving front driven by the calculated 2009 – 2018 calving rate. The results of these simulations show that the response of the glacier to the applied calving rate is in line with its observed evolution over this period. We also present the results of further experiments designed to examine the mechanisms and controls on the calving retreat.

How to cite: Trevers, M., Payne, T., Cornford, S., and Hogg, A.: Modelling Jakobshavn Isbrae from 2009 to 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21999, https://doi.org/10.5194/egusphere-egu2020-21999, 2020.

EGU2020-15790 | Displays | CR5.7

Deriving a Physically-Based Calving Rate Law for Marine Ice-Cliff Instability

Anna Crawford, Joe Todd, Doug Benn, Jan Åström, and Thomas Zwinger

Rapid grounding line retreat at marine-terminating glaciers could expose ice cliffs with heights greater than those on observational record. However, the finite strength of ice places a limit on the height of subareal cliffs. It is proposed that marine ice-cliff instability (MICI) will begin once a stable height threshold is exceeded. If a glacier is situated over a retrograde slope, as is the case for Thwaites Glacier and much of the West Antarctic Ice Sheet, MICI can be expected to accelerate as retreat progresses and increasingly tall and unstable ice cliffs are formed. This is consequential for global sea level rise, yet large uncertainties remain in the prediction of MICI retreat rates.

We investigate MICI by pairing the full Stokes continuum model Elmer/Ice and the Helsinki Discrete Element Model (HiDEM). Viscous flow, simulated in Elmer/Ice, is found to be a necessary pre-condition for MICI collapse. Forward advance and bulging lead to ice-front instability and pervasive crevassing in HiDEM. This culminates in full-thickness calving events. We do not observe calving at ice faces prior to viscous deformation. HiDEM simulations that implement viscous flow (HiDEM-ve) also show forward advance and waterline bulging, similar to the Elmer/Ice simulations. However, the importance of granular shear is highlighted by pronounced shear bands and patterns of surface lowering in HiDEM-ve output. These results emphasize the importance and complexity of viscous and brittle process interaction during MICI.

A simulation matrix of grounded termini shows that calving frequency and magnitude increase with the thickness of the calving front. The time required for viscous flow to recreate unstable conditions is influenced by thickness as well as ice temperature and basal friction. Simulations of buoyant termini are seen to calve through basal-crevassing and block-rotation, as opposed to incising surface-crevasses. Lastly, we observe that buttressing mélange can suppress retreat rate if a sufficient resistive force is delivered to the calving front. A physically-based law for MICI retreat rate is derived from our simulation matrix; this calving rate law can be incorporated into large-scale ice sheet models to constrain projections of Antarctic retreat and associated global sea level rise. Our results will also be used to investigate the future retreat of Thwaites Glacier, which is vulnerable to MICI due to a retreating grounding line, fragile floating ice shelf, and precarious positioning above an overdeepening basin.

How to cite: Crawford, A., Todd, J., Benn, D., Åström, J., and Zwinger, T.: Deriving a Physically-Based Calving Rate Law for Marine Ice-Cliff Instability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15790, https://doi.org/10.5194/egusphere-egu2020-15790, 2020.

EGU2020-1607 | Displays | CR5.7

A 3D full-Stokes model of Store Glacier, Greenland, with coupling of ice flow, subglacial hydrology, submarine melting and calving

Samuel Cook, Poul Christoffersen, Joe Todd, Donald Slater, Nolwenn Chauché, and Martin Truffer

Tidewater glaciers are complex systems, which present numerous modelling challenges with regards to integrating a multitude of environmental processes spanning different timescales. At the same time, an accurate representation of these systems in models is critical to being able to effectively predict the evolution of the Greenland Ice Sheet and the resulting sea-level rise. In this study, we present results from numerical simulations of Store Glacier in West Greenland that couple ice flow modelled by Elmer/Ice with subglacial hydrology modelled by GlaDS and submarine melting represented with a simple plume model forced by hydrographic observations. The simulations capture the seasonal evolution of the subglacial drainage system and the glacier’s response, and also include the influence of plume-induced ice front melting on calving and buttressing from ice melange present in winter and spring.

Through running the model for a 6-year period from 2012 to 2017, covering both high- and low-melt years, we find inputs of surface meltwater to the subglacial system establishes channelised subglacial drainage with channels >1 m2 extending 30-60 km inland depending on the amount of supraglacial runoff evacuated subglacially. The growth of channels is, however, not sufficiently fast to accommodate all inputs of meltwater from the surface, which means that basal water pressures are generally higher in warmer summers compared to cooler summers and lowest in winter months. As a result, the simulated flow of Store Glacier is such that velocities peak in warmer summers, though we suggest that higher surface melt levels may lead to sufficient channelisation for a widespread low-water-pressure system to evolve, which would reduce summer velocities. The results indicate that Greenland’s contribution to sea-level rise is sensitive to the evolution of the subglacial drainage system and especially the ability of channels to grow and accommodate surface meltwater effectively. We also posit that the pattern of plume melting encourages further calving by creating an indented calving front with ‘headlands’ that are laterally unsupported and therefore more vulnerable to collapse. We validate our simulations with a three-week record of iceberg calving events gathered using a terrestrial radar interferometer installed near the calving terminus of Store Glacier.

How to cite: Cook, S., Christoffersen, P., Todd, J., Slater, D., Chauché, N., and Truffer, M.: A 3D full-Stokes model of Store Glacier, Greenland, with coupling of ice flow, subglacial hydrology, submarine melting and calving, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1607, https://doi.org/10.5194/egusphere-egu2020-1607, 2020.

   The Greenland ice sheet is currently contributing to global sea level at an approximate rate of 0.8 mm/yr. Ice mass loss of Greenland is primarily due to both thinning and retreat of outlet glaciers. For enhanced calving events, detail dynamics characteristics of hydrological and kinematic precursors and underlying mechanisms which control the development of ice calving remain poorly understood, especially in the absence of high-resolution remote sensing observations. On July 26 2017, a calving event took place along a pre-existing rift in Petermann glacier, northern Greenland, which removed partly of the glacier tongue and formed a tabular iceberg 5 km long. In this study, we used high-temporal satellite remote sensing data to detect changes in ice-flow speed, melt ponds and ice mélange during May and July. These hydrological and kinematic dynamics derived from Sentinel-1/2 satellite images with sub-weekly acquisition repeat cycles can be utilized as retreat precursors to characterize the detailed calving process. Moreover, the stress field and analytical damage solution were calculated by coupling the remote sensing observations with SSA ice sheet model to explain the dynamics mechanism. Our preliminary results show that the ice speed in dense observation reached to 30 m/d on the eve of the calving, which is roughly 10 times quicker than usual ice velocity. Additionally, there exited obviously abnormal stress distribution in crack region. And the landfast sea ice and ice mélange transformed into open water that the  backscatter coefficient decreased to 28 dB. The extent of melt pond reached the peak about 30 square kilometers coverage in duration month of calving event. It is inferred that this calving event of Petermann glacier may be related to weakening of sea ice and ice mélange lost the buttressing for ice glacier terminate, tributary glacier extrusion, related with meltwater infiltrated crevasses. Therefore, dense remote sensing observations and numerical modeling in ice flow system make it possible for early waring and projecting glacier calving in the future.

Key words: Iceberg Calving Precursors, Petermann Glacier, High Resolution Remote Sensing, SSA modeling

How to cite: Li, D. and Jiang, L.: Hydrological and Kinematic Precursors of Iceberg Calving at Petermann Glacier in Northern Greenland Observed High-temporal Resolution Sentinel-2 Images, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7831, https://doi.org/10.5194/egusphere-egu2020-7831, 2020.

CR5.8 – Hydrology of ice shelves, ice sheets and glaciers - from the surface to the base

EGU2020-6190 | Displays | CR5.8

Ice-shelf instability due to surface meltwater systems on the George VI Ice Shelf

Alison F. Banwell, Rebecca Dell, Devon Dunmire, Douglas MacAyeal, Laura A. Stevens, and Ian C. Willis

 

The evolution of surface and shallow subsurface meltwater bodies across Antarctic ice shelves has important implicationsfor their (in)stability, as demonstrated by the 2002 rapid collapse of the Larsen B Ice Shelf. Ice-shelf break-up may be triggered by stress variations associated with meltwater movement, ponding and drainage, causing ice-shelf flexure and fracture. We have recently begun a four year, jointly-funded US-NSF / UK-NERC project that will provide important geophysical insights into the stability of the George VI Ice Shelf on the Antarctic Peninsula, where hundreds of surface lakes form each summer.

In November 2019, we deployed global positioning systems, pressure transducers, automatic weather stations, and in-ice thermistor strings to record ice-shelf flexure, surface water depths, and surface and subsurface melting, respectively, in and around several surface lakes. Next austral summer (November 2020), we also plan to record fracture seismicity with a passive seismometer deployment, and to conduct ground penetrating radar surveys to detect subsurface water. Instruments, which are all within ~30 km of BAS's Fossil Bluff Station, will remain on the ice shelf until January 2022, resulting in a 27-month observational record in total.

Here, we report results of satellite image analysis of surface and shallow subsurface meltwater bodies, together with preliminary field and modelling results associated with our project. Using NDWIice thresholds applied to Landsat 8, Sentinel-2 and WorldView optical imagery, we show how patterns of surface meltwater evolve within and between summer melt seasons. Using Sentinel-1 SAR imagery and a convolutional neural network technique, we detect and track bodies of shallow subsurface water and show how they relate to patterns of surface water. We also report on field reconnaissance surveys made to two dolines (drained lake basins) on the ice shelf, and present a simple model to describe the process of doline formation. Throughout the project, we will combine field and remotely sensed data to extend and validate our existing approach to modelling ice-shelf flexure and stress, and possible ‘Larsen-B style’ ice-shelf instability and break-up at less geographically confined ice shelves.

How to cite: Banwell, A. F., Dell, R., Dunmire, D., MacAyeal, D., Stevens, L. A., and Willis, I. C.: Ice-shelf instability due to surface meltwater systems on the George VI Ice Shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6190, https://doi.org/10.5194/egusphere-egu2020-6190, 2020.

EGU2020-7574 | Displays | CR5.8

Modelling perennial firn aquifers in the Antarctic Peninsula

Jan Melchior van Wessem, Michiel van den Broeke, Christian Steger, Nander Wever, and Stefan Ligtenberg

We predict the location of perennial firn aquifers (PFAs) in the Antarctic Peninsula using the updated regional atmospheric climate model RACMO2.3p2, that is specifically adapted for use over the polar regions. With RACMO2 output we force two sophisticated firn models, IMAU-FDM and SNOWPACK, with surface mass fluxes and surface energy fluxes, respectively. These firn models explicitly calculate processes in the snowpack, such as densification, meltwater penetration, refreezing, retention and runoff.

In this presentation, we focus on the Antarctic Peninsula (AP), where conditions are favorable for the formation of PFAs: there is both sufficient meltwater production and snowfall to store the meltwater in the firn during winter without refreezing, as the fresh snow insulates the meltwater from the winter cold wave. These conditions are similar to those locations where PFAs were discovered in Greenland and Svalbard.

While slightly different in behavior, both firn models calculate PFAs on Wilkins ice shelf and the northwestern AP mountain range, but also near the grounding lines of unstable or disintegrated ice shelves such as Prince Gustav, Larsen B and Wordie. The PFAs exist in different forms, e.g. long-lasting, shallow, deep or multi-layer, and are sensitive to the magnitude and timing of atmospheric forcing conditions. We carefully explore processes controlling their formation and/or longevity, discuss their implications for ice shelf stability, and their potential to exist elsewhere in Antarctica.

How to cite: van Wessem, J. M., van den Broeke, M., Steger, C., Wever, N., and Ligtenberg, S.: Modelling perennial firn aquifers in the Antarctic Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7574, https://doi.org/10.5194/egusphere-egu2020-7574, 2020.

EGU2020-15912 | Displays | CR5.8

How does the meltwater flow? Retention and refreezing in firn on ice sheets and ice shelves

Ruth Mottram, Baptiste Vandecrux, Martin Olesen, Fredrik Boberg, Nicolaj Hansen, Peter Langen, and Robert Fausto and the RetMIP contributors

Mass loss from glacier surface melt is buffered by percolation and refreezing in the underlying snowpack, processes of particular importance in the percolation zone of the Greenland ice sheet and increasingly in Antarctica under a warming climate. Retention and refreezing is dependent on a number of micro-scale factors such as snow grain size, density and temperature that are heavily parameterized in models. Melt and snowfall in preceding seasons are also important in determining retention rates in the current season due to initialization of the snowpack .

In the retention model intercomparison project (RetMIP) we use a common atmospheric forcing from the HIRHAM5 regional climate model to drive participating  models, to study the effect of different internal parameterisations. We compare 9 different 1D models and four 2D models with each other and with observations from 4 key field sites. We show that initialisation of snowpack models is important but evolution of retention through time is strongly determined by melt rates.

Models that explicitly account for deep meltwater percolation tend to overestimate percolation depth and consequently firn temperature at the percolation and ice slab sites although they simulate accurately the recharge of the firn aquifer. Models using Darcy’s law and bucket scheme compare favourably to observations at the percolation site but only the Darcy models accurately simulate firn temperature and thus meltwater percolation at the ice slab site. We find that Eulerian models that transfer firn through fixed layers, diffuse over time the gradients in firn temperature and density. No model outperforms all others at our four test sites indicating that all models have potential for development.

A first look at Antarctic firn processes emphasises the importance of long spin-up times to initialise the snowpack and as the ice sheet surface evolves in the future parameterising the specific Antarctic retention process is likely to become more important.

How to cite: Mottram, R., Vandecrux, B., Olesen, M., Boberg, F., Hansen, N., Langen, P., and Fausto, R. and the RetMIP contributors: How does the meltwater flow? Retention and refreezing in firn on ice sheets and ice shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15912, https://doi.org/10.5194/egusphere-egu2020-15912, 2020.

EGU2020-8344 | Displays | CR5.8

Simulating Antarctic subglacial hydrology processes underneath Pine Island Glacier, West Antarctica, using GlaDS model in Elmer/Ice

yufang zhang, John Moore, Michael Wolovick, Rupert Gladstone, Thomas Zwinger, and xiaoran guo

Abstract: Very little is known about the subglacial hydrologic system under the Antarctic Ice Sheet due to the difficulty of directly observing the bottom of the ice sheet. Hydrology modeling is a powerful tool to simulate the spatial distribution of crucial hydrologic properties under the ice sheet. Here, we use the state-of-art two-dimensional Glacier Drainage System model (GlaDS) to simulate both distributed sheet flow and continuous channels under Pine Island Glacier (PIG), West Antarctica, one of the largest contributors to sea level rise in Antarctica.

We adopt an unstructured triangular mesh which enables channels to form along element edges. We drive the model with meltwater computed from an inversion and steady temperature simulation of PIG using a Stokes flow ice dynamic model. Our domain comprises the full PIG catchment. We aim to study the pattern and development of water pressure, hydraulic potential, water sheet thickness and discharge, as well as channel area and flux, which together describe the state of the basal system.

Our results for hydraulic potential correctly route water towards the grounding line, while we find near-zero effective pressure underneath the main trunk of PIG, consistent with the low basal drag and low driving stress there. This has implications for the representation of sliding in ice dynamic models: typical assumptions about hydrology connectivity to the ocean will overestimate effective pressure. When run forward in time, efficient channels evolve near the grounding line indicating an efficient drainage system where water fluxes are high in the downstream part of the PIG.

By applying GlaDS to a real marine ice sheet catchment we can better understand how basal hydrology modulates ice dynamics through basal sliding. We plan to compare our model predictions of effective pressure and drainage system with driving stress and inversions of basal drag. This will allow us to see the relationship between basal hydrology and basal sliding under PIG, and provide us better tools to predict the evolution of the region in view of future climate scenarios. Moving forward, we plan to couple the hydrology model with the ice dynamics model to make more accurate projections of sea level rise from PIG.

Key Words: West Antarctica, subglacial hydrology, drainage system, GlaDS, Elmer/Ice, Pine Island Glacier

How to cite: zhang, Y., Moore, J., Wolovick, M., Gladstone, R., Zwinger, T., and guo, X.: Simulating Antarctic subglacial hydrology processes underneath Pine Island Glacier, West Antarctica, using GlaDS model in Elmer/Ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8344, https://doi.org/10.5194/egusphere-egu2020-8344, 2020.

EGU2020-19947 | Displays | CR5.8

The Petermann Ice Shelf Estuary and its impact on ice-shelf stability

Alexandra Boghosian, Lincoln Pitcher, Laurence Smith, and Robin Bell

In a warming world, increased meltwater will form on Antarctica’s ice shelves. The fate of this meltwater will be critical to future ice-shelf and ice-sheet stability. Two main observations define the current theoretical framework for understanding the influence of surface hydrology on ice-shelf stability. The first is the collapse West Antarctica’s Larsen B Ice Shelf that was triggered by the formation of thousands of surface ponds atop the ice shelf. The second is the observation of a waterfall on the Nansen Ice Shelf, in East Antarctica, that is hypothesized to protect the ice shelf from hydrofracture by removing meltwater from the ice-shelf surface.

We present a third process that couples ice-shelf hydrology to atmospheric and ocean forcing: the development of an ice-shelf estuary on the Petermann Ice Shelf in northwest Greenland.  High-resolution imagery and digital elevation models (DEMs) shows that channelized surface meltwater on the Petermann Ice Shelf in northwest Greenland incises into underlying ice to form an estuary that propagates fractures along the ice shelf. The estuary at the front of the Petermann Ice Shelf is indicated by the convergence of sea ice at the river mouth, the upstream transport of sea ice in the channel as far as 460 m from the calving front, and the persistence of water in the channel following the end of seasonal surface melt. Between 2013 and 2018, the estuarine reach of the river tripled in width and a 1.5 km longitudinal crack propagated along the bottom of the channel. The Petermann Ice Shelf Estuary forms on top of a basal channel, where basal melting has led to ice-shelf thinning, and the creation of the linear surface depression in which the estuary forms.

The Petermann Estuary may be the first of several ice-shelf estuaries to develop in a warming climate. Widespread surface melting on ice shelves in Greenland and Antarctica increases the urgency to determine the influence of surface hydrology on ice-shelf stability. We hypothesize that surface rivers may initially buffer ice shelves from collapse by terminating in waterfalls and preventing the formation of damaging lakes. However, with increased meltwater transport across ice shelves, channels can incise to sea level and establish estuaries. Once an estuary is established, estuarine weakening can lead to fracture propagation and enhanced calving, destabilizing ice-shelves, and increased ice-sheet mass loss.

How to cite: Boghosian, A., Pitcher, L., Smith, L., and Bell, R.: The Petermann Ice Shelf Estuary and its impact on ice-shelf stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19947, https://doi.org/10.5194/egusphere-egu2020-19947, 2020.

EGU2020-12775 | Displays | CR5.8

Estimating the configuration of the subglacial drainage system under a mountain glacier in St. Elias Mountains, Yukon

Gabriela Clara Racz, Christian Schoof, Camilo Rada, Robert Koschitzki, Eldad Haber, and Gwenn Flowers

Numerous studies have documented that water at the ice-bed interface can affect ice flow dynamics of both, mountain glaciers and the Greenland ice sheet. Water at the bed is routed through a complex network of conduits that form a subglacial drainage system. The subglacial drainage system evolves over the melt season in response to the changes in the meltwater supply. However, it is challenging to study due to the inaccessibility of the glacier bed. We use an extensive near-bed water pressure data set from an ablation zone of a small, polythermal, mountain glacier in St. Elias Mountains, Yukon.  Pressure sensors, that exhibit common diurnal variations, are considered to be connected to a hydraulically active drainage system. 

We use a simplified two-dimensional continuum version of the subglacial drainage model with an additional assumption that changes in drainage configuration are negligible over a short time period. Spatially varying permeability function is used as a proxy for the subglacial drainage configuration, assuming that the areas of high (low) permeability correspond to the areas that are connected (disconnected) to a hydraulically active system.  In order to study the evolution of the subglacial drainage system over the melt season, we divide the melt season in a series of short time periods. We then use the inverse model to estimate the permeability function for each of these time periods. Continuity is ensured by using, respectively, the final pressure distribution and the estimated permeability function of the previous period, as the initial condition and the a priori estimate for the consequent time period.

How to cite: Racz, G. C., Schoof, C., Rada, C., Koschitzki, R., Haber, E., and Flowers, G.: Estimating the configuration of the subglacial drainage system under a mountain glacier in St. Elias Mountains, Yukon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12775, https://doi.org/10.5194/egusphere-egu2020-12775, 2020.

EGU2020-16998 | Displays | CR5.8

Microbial abundance and transport in glacial near-surface meltwater

Ian Stevens, Tristram Irvine-Fynn, Arwyn Edwards, Philip Porter, Joseph Cook, Tom Holt, Brian Moorman, Andy Hodson, and Andrew Mitchell

Glacier surfaces are active microbial ecosystems which contribute to melt feedback cycles and biogeochemical processes. Despite this recognition, there is a lack of knowledge regarding the transport dynamics and residence time of microbes in this supraglacial habitat. Throughout the ablation season, meltwater is generated across a glacier’s surface and flows through the porous near-surface weathering crust before entering the channelised supraglacial network. Within the weathering crust, solar radiation provides a “photic zone” which, combined with nutrient availability, is conducive for microbial activity. The water flow through this porous near-surface layer provides a transport mechanism for these microbes. However, the nature of controls upon this phenomenon remain unexplored, despite the relevance for cellular export to downstream ecosystems, glacier surface albedo and biogeochemical cycling.

To determine potential controls on microbial transport in the weathering crust, we present 913 measurements of microbial cell abundance in supraglacial meltwaters from 11 glaciers across the northern hemisphere. Each measurement is coupled with weathering crust hydraulic conductivity or stream discharge. These data reveal a mean microbial abundance of 2.2 × 104 cells mL-1 (with a range of 103 – 106) in supraglacial meltwaters within the weathering crust and stream channels. Modal microbe size was 1 – 2 μm (56 % of microbes), with 89 % of microbes smaller than 4 μm. No substantiated difference in size distributions between weathering crust and stream meltwaters were observed. No correlation between microbial abundance and near-surface hydraulic conductivity or stream discharge were observed, either across the entire dataset or when considered on a glacier-by-glacier basis. At three glaciers, water temperature and electrical conductivity (a proxy measure for ionic load) were also recorded; but we observe no correlation between these two variables and microbial abundance. Our data suggests weathering crust microbe abundance is consistent across differing glacial environments, and the concentrations entrained in the near-surface equal those seen in supraglacial streams. As such, despite the low transfer rate of meltwater, there appears to be limited evidence for substantial storage or accumulation of biomass in the near-surface weathering crust. Moreover, microbe entrainment does not appear to be driven by primary hydrological controls. Assuming that once liberated within the weathering crust entrained microbes reach channelised supraglacial networks, we estimate a delivery of 1.1 × 109 kg C a-1 to downstream environments globally (excluding Antarctica) to 2100, using existing discharge forecasts. This study represents a crucial first step in examining microbial abundance within, and transport across glacier surfaces and their potential role in biogeochemical process-feedbacks and the inoculation of downstream environments.

How to cite: Stevens, I., Irvine-Fynn, T., Edwards, A., Porter, P., Cook, J., Holt, T., Moorman, B., Hodson, A., and Mitchell, A.: Microbial abundance and transport in glacial near-surface meltwater , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16998, https://doi.org/10.5194/egusphere-egu2020-16998, 2020.

EGU2020-377 | Displays | CR5.8

Winter draining lakes on the Greenland ice sheet observed by Sentinel-1

Corinne Benedek and Ian Willis

Supraglacial lakes on the Greenland Ice Sheet influence surface mass balance, the delivery of water from the surface to the bed, and the rate of basal sliding.  Summertime lake drainage behavior has been catalogued thoroughly through the use of optical remote sensing with a variety of satellites.  Radar results from Operation IceBridge demonstrated the presence of liquid water buried in lakes under ice lids but this platform is limited in its capability to examine short-term changes over the winter season.  This study describes the drainage of multiple buried lakes through the winter season using Sentinel-1 C-Band SAR.  Sudden positive anomalous changes in mean backscatter of surface lakes that are sustained over time are used to pick out wintertime (October through May) lake drainages over a four-year study period.  These changes are confirmed using late-Autumn and early-Spring Landsat-8 photoclinometry changes.  Drainages are detected from November through February, pointing to the likelihood of water injection to the bed through the winter season.  Our automated techniques involve quantifying patterns and trends in SAR backscatter and are also being developed to contribute to our understanding of water storage vs. refreezing in lakes and firn on the surface and in the shallow sub-surface regions of the Greenland Ice Sheet throughout the year.

How to cite: Benedek, C. and Willis, I.: Winter draining lakes on the Greenland ice sheet observed by Sentinel-1, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-377, https://doi.org/10.5194/egusphere-egu2020-377, 2020.

EGU2020-1427 | Displays | CR5.8 | Highlight

Evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica

Jennifer Arthur, Chris Stokes, Stewart Jamieson, Rachel Carr, and Amber Leeson

Supraglacial lakes (SGLs) enhance surface melting and their development and subsequent drainage can flex and fracture ice shelves, leading to their disintegration. However, the seasonal evolution of SGLs and their potential influence on ice shelf stability in East Antarctica remains poorly understood, despite a number of potentially vulnerable ice shelves. Using optical satellite imagery, climate reanalysis data and surface melt predicted by a regional climate model, we provide the first multi-year analysis (1974-2019) of seasonal SGL evolution on Shackleton Ice Shelf in Queen Mary Land, which is Antarctica’s northernmost remaining ice shelf. We mapped >43,000 lakes on the ice shelf and >5,000 lakes on grounded ice over the 45-year analysis period, some of which developed up to 12 km inland from the grounding line. Lakes clustered around the ice shelf grounding zone are strongly linked to the presence of blue ice and exposed rock, associated with an albedo-lowering melt-enhancing feedback. Lakes either drain supraglacially, refreeze at the end of the melt season, or shrink in-situ. Furthermore, we observe some relatively rapid (≤ 7 days) lake drainage events and infer that some lakes may be draining by hydrofracture. Our observations suggest that enhanced surface meltwater could increase the vulnerability of East Antarctic ice shelves already preconditioned for hydrofracture, namely those experiencing high surface melt rates, firn air depletion, and extensional stress regimes with minimum topographic confinement. Our results could be used to constrain simulations of current melt conditions on the ice shelf and to investigate the impact of increased surface melting on future ice shelf stability.

How to cite: Arthur, J., Stokes, C., Jamieson, S., Carr, R., and Leeson, A.: Evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1427, https://doi.org/10.5194/egusphere-egu2020-1427, 2020.

EGU2020-1616 | Displays | CR5.8

Controls on crevasse water transmission to the bed of an ice sheet from remotely sensed datasets

Tom Chudley, Poul Christoffersen, Sam Doyle, Tom Dowling, Marion Bougamont, Charlie Schoonman, Rob Law, and Bryn Hubbard

Surface meltwater is transmitted to the bed of the Greenland Ice Sheet via supraglacial lake drainages, moulins, and crevasses. Of these, comparatively little research has been performed on the melt infiltration occurring in crevasse fields, which are widespread  in fast-flowing, marine-terminating sectors of the ice sheet. Here, we explore the relationships between crevassing, incidence of surface meltwater, and glacier dynamics at a fast-flowing, marine-terminating sector of West Greenland. Data were collected at high spatial resolution from unmanned aerial vehicle (UAV) surveys on Store Glacier, Greenland, in July 2018. Crevasses and surface water were identified using an object-based machine learning classifier, and strain rates and subsequent stress fields were derived from feature-tracked velocities. Contemporaneous observations of  crevasses and surface water on a larger regional scale were made using ArcticDEM and Sentinel-2 data processed in the Google Earth Engine cloud-based geospatial analysis platform, while stress fields are derived from MEaSUREs velocity data. We find that, whilst previous studies have focussed on relationships between crevassing and stress regime through yield criterion such as the Von Mises stress, we can additionally link the observed spatial distribution of surface meltwater over crevasse fields to the mean stress (defined as the arithmetic mean of the maximum and minimum stress). Crevasse fields existing in tensile mean stress regimes were less likely to exhibit ponded meltwater through a melt season, which we interpret as meltwater being able to continuously drain into the englacial system. Conversely, crevasse fields in compressive mean stress regimes were more likely to exhibit ponded meltwater, which we interpret to be as a result of englacial conduit closure. We show that in these compressive regions, water transfer takes place via intermittent drainage events (i.e. hydrofracture), as envisaged in linear elastic fracture mechanics (LEFM) models. Hence, stress regime can inform spatially heterogeneous styles of crevasse drainage across the ablation zone of an ice sheet: a continuous, low-intensity mode in extensional regimes, in contrast to an episodic, high-intensity mode in compressional regimes. These processes may have distinctly different impacts on basal processes, including subglacial drainage efficiency, diurnal variability, and cryo-hydrologic warming.

How to cite: Chudley, T., Christoffersen, P., Doyle, S., Dowling, T., Bougamont, M., Schoonman, C., Law, R., and Hubbard, B.: Controls on crevasse water transmission to the bed of an ice sheet from remotely sensed datasets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1616, https://doi.org/10.5194/egusphere-egu2020-1616, 2020.

EGU2020-2226 | Displays | CR5.8

Modelling the basal hydrology under the Greenland Ice Sheet

Alexander Vanhulle, Sébastien Le Clec’h, and Philippe Huybrechts

Subglacial hydrology plays an important role in the evolution of ice dynamics. Primarily, it affects basal processes such as basal sliding. Further, subglacial water exiting a calving front incites submarine melt, increasing calving, resulting in a thinning of the interior ice sheet. Knowledge of it is therefore crucial towards the development and improvement of ice sheet models. We implement a model representing the routing of subglacial water below the Greenland ice sheet in either a one, four or eight directional manner. Due to its computational efficiency, the model is suited for coupling with continental scale ice sheet models on very high resolutions (e.g. 150 m).

Routing depends on the hydraulic potential of individual grid cells which is therefore heavily dependent on accurate estimates of the ice thickness as well as the grid utilized. Sensitivity analyses brought to life that the routing exhibits artefacts resulting in significant flow diversions on high resolutions if the gradients are only considered over the distance of a single grid cell, this is overcome by incorporating a smoothing procedure.

With the basal water model in place and input of the basal melt rate from the VUB Greenland Ice Sheet Model (GISM) as well as runoff input from the Modèle Athmospherique Régional (MAR), we calculate the inflow of freshwater to several reference fjords for the last thirty years and investigate its temporal and spatial patterns. Jakobshavn Isbrae experiences by far the most freshwater inflow compared to the other reference fjords. Despite limited runoff in the northeast of Greenland, high basal melt rates and a significant catchment area provide the outlets of the Northeast Greenland Ice Stream (NEGIS) with substantial inflow too.

How to cite: Vanhulle, A., Le Clec’h, S., and Huybrechts, P.: Modelling the basal hydrology under the Greenland Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2226, https://doi.org/10.5194/egusphere-egu2020-2226, 2020.

EGU2020-2441 | Displays | CR5.8

Evolution of supraglacial lakes on the Larsen B ice shelf in the decades before it collapsed
not presented

Amber Leeson, Elliott Foster, Amiee Rice, Noel Gourmelen, and Melchior van Wessem

The Larsen B ice shelf collapsed in 2002 losing an area twice the size of Greater London to the sea (3000 km2), in an event associated with widespread supraglacial lake drainage. Here, we use optical and radar satellite imagery to investigate the evolution of the ice shelf’s lakes in the decades preceding collapse. We find 1) that lakes spread southwards in the preceding decades at a rate commensurate with meltwater saturation of the shelf surface, 2) no trend in lake size, suggesting an active supraglacial drainage network which evacuated excess water off the shelf and 3) lakes mostly re-freeze in winter but the few lakes that do drain are associated with ice break up 2-4 years later. Given the relative scale of lake drainage and shelf break up, however, it is not clear from our data whether lake drainage is more likely a cause, or an effect, of ice shelf collapse.

How to cite: Leeson, A., Foster, E., Rice, A., Gourmelen, N., and van Wessem, M.: Evolution of supraglacial lakes on the Larsen B ice shelf in the decades before it collapsed, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2441, https://doi.org/10.5194/egusphere-egu2020-2441, 2020.

EGU2020-7540 | Displays | CR5.8

Coupling subglacial hydrology to basal friction in an Antarctic ice sheet model

Elise Kazmierczak, Lars Zipf, and Frank Pattyn

Due to the lack of direct observations, subglacial hydrology is still marginally considered in Antarctic ice sheet modelling studies, albeit that several approaches exist (e.g., LeBrocq, Bueler and Van Pelt). Subglacial hydrology impacts basal friction through a reduction in effective pressure and through changing properties of subglacial sediments, both factors influencing the lubrication at the bottom of the ice sheet. Several approaches exist to represent subglacial hydrology in ice sheet models (Bueler and Brown, 2009, Goeller et al., 2013) and are generally coupled to either a Coulomb or a Weertman friction law. However, the type of subglacial process determines to a large extent the sensitivity of Antarctic mass change (Sun et al, submitted).

 

In this study we investigate the sensitivity of subglacial dynamics on the behaviour of the Antarctic ice sheet on centennial time scales. For this purpose we employ a subglacial hydrology model for subglacial water routing (Lebrocq et al., 2009) coupled to a thermomechanical ice-sheet model (f.ETISh; Pattyn, 2017). We consider different parametrizations and representations of effective pressure and till water content at the base.  We also consider the combination of different friction laws and hydrological models (sheet flow, till deformation) depending on estimates of the subglacial conditions of the Antarctic ice sheet. Results show that the way of coupling subglacial hydrology influences the sensitivity of the ice-sheet system on centennial time scales. However, the type and power of the friction law (Coulomb versus Weertman)  has the most dominant impact on ice sheet sensitivity.

How to cite: Kazmierczak, E., Zipf, L., and Pattyn, F.: Coupling subglacial hydrology to basal friction in an Antarctic ice sheet model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7540, https://doi.org/10.5194/egusphere-egu2020-7540, 2020.

EGU2020-9856 | Displays | CR5.8

Temporal variations in the surface hydrology across Antarctic ice shelves

Rebecca Dell, Ian Willis, Neil Arnold, Alison Banwell, Hamish Pritchard, and Anna Ruth Halberstadt

Widespread surface meltwater systems have been identified across numerous Antarctic ice shelves and have been implicated in their possible instability and eventual breakup. It is crucial to better understand the seasonal and year-to-year development of these surface meltwater systems, which comprise saturated firn (slush) as well as distinct water bodies (lakes and streams). It has been suggested that repeated melting and re-freezing of the surface firn pack over successive years reduces the firn air content, and therefore its porosity, encouraging the formation of surface water bodies over time. Firn air depletion and the formation of surface water bodies may contribute to ice shelf instability, as the ice becomes increasingly susceptible to hydrofracture.

Here, we use Google Earth Engine to investigate the distributions of slush and deeper water bodies across all Antarctic ice shelves known to have surface melt, to quantify how surface meltwater systems evolve both seasonally and over successive summers. To do this, we use supervised classification of Sentinel-2 and Landsat 7/8 imagery to guide the selection of suitable NDWIice thresholds for both the detection of slush and deep surface meltwater. Preliminary results for the George VI Ice Shelf between 2000 and 2017 reveal seasonal patterns in the overall extent of surface meltwater, and the overall meltwater extent typically peaks between January and March each year. The 2009-2010 melt season was characterised by significant melt, and over the course of the melt season the proportion of the overall surface meltwater extent that was held within deep water bodies varied between 0 % (November) and 60 % (January). An increase in the proportion of deep water vs. slush typically aligns with warmer air surface temperatures and, therefore periods of more intense melt.

How to cite: Dell, R., Willis, I., Arnold, N., Banwell, A., Pritchard, H., and Halberstadt, A. R.: Temporal variations in the surface hydrology across Antarctic ice shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9856, https://doi.org/10.5194/egusphere-egu2020-9856, 2020.

EGU2020-10677 | Displays | CR5.8

Surface lake depths on an Antarctic ice shelf: comparing in-situ measurements with ground and satellite multispectral methods

Ian Willis, Alison Banwell, Grant Macdonald, Michael Willis, and Doug MacAyeal

There is growing interest in surface and shallow subsurface water bodies across Antarctic ice shelves as they impact the ice shelf mass balance. Additionally, the filling and draining of lakes has the potential to flex and fracture ice shelves, which may even lead to their catastrophic break up. The study of lakes on ice shelf surfaces typically uses optical satellite imagery to delineate their area and a parameterised physically-based light attenuation theory to calculate their depths. The approach has been developed and validated using various data sets collected on the Greenland Ice Sheet, but so far the approach has not been validated for Antarctic ice shelves. Here we use simultaneous field measurements of lake water depth and surface spectral properties (red, blue, green, panchromatic), to parameterise the light attenuation theory for use during the filling and draining of shallow lakes on the McMurdo Ice Shelf during the 2016/2017 austral summer. We then apply the approach to calculate lake areas, depths and volumes across several water bodies observed in high resolution Worldview imagery, which helps validate the approach to calculating water volumes across a larger part of the ice shelf using Landsat 8 imagery. Results suggest that using parameter values relevant to the Greenland Ice Sheet may bias the calculation of water volumes when applied to Antarctic ice shelves, and we suggest more appropriate values.

How to cite: Willis, I., Banwell, A., Macdonald, G., Willis, M., and MacAyeal, D.: Surface lake depths on an Antarctic ice shelf: comparing in-situ measurements with ground and satellite multispectral methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10677, https://doi.org/10.5194/egusphere-egu2020-10677, 2020.

EGU2020-10744 | Displays | CR5.8

Supraglacial and subglacial meltwater routing in Kongsfjord basin, Svalbard

Chloé Scholzen, Thomas Vikhamar Schuler, and Adrien Gilbert

In tidewater glacier fjords, the amount, the spatial distribution, and the timing of meltwater entering the subglacial hydrological system play a key role in modulating ice flow dynamics, as well as in impacting adjacent marine ecosystems. This study aims to describe how meltwater journeys through the polythermal glaciers of Kongsfjord basin in Svalbard, Norway. Our methodology involves the use of a surface runoff timeseries (2003-2017) from a coupled surface-energy-balance-snow model forced by a regional climate model (HIRLAM). Using a program for flow pathways analysis in DEMs (TopoToolbox), we generate a map of surface meltwater streams and drainage catchment areas. Other supraglacial features such as melt lakes, moulins and crevasses are manually detected from satellite imagery. These serve as basis to create four different setups of water input to a subglacial drainage model (GlaDS): (1) a spatially continuous input that equals the surface runoff, (2) a discrete input where the total surface runoff over the whole Kongsfjord basin is equally distributed between moulins, (3) a discrete input where upstream catchment areas are taken into account to weight the runoff drained into each moulin, and (4) a hybrid configuration of (1) and (3) where in crevassed areas the input equals the surface runoff, while in non-crevasses areas moulins are fed by upstream catchment runoff. The subglacial drainage model, which allows for meltwater to flow through both an inefficient distributed network of linked cavities, and a more efficient channelized system, yields spatiotemporal information on basal water pressure, sheet discharge and channel discharge, as well as on channel location. Results for the four water input setups are compared, and we discuss the relevance of using a more realistic configuration of meltwater recharge when modeling hydrological systems underneath glaciers. Finally, based on our model outputs, we provide seasonal maps of Kongsfjord basin’s subglacial hydrology that show the preferential flow path of basal water and through which glacier outlet meltwater is released into the fjord.  

How to cite: Scholzen, C., Vikhamar Schuler, T., and Gilbert, A.: Supraglacial and subglacial meltwater routing in Kongsfjord basin, Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10744, https://doi.org/10.5194/egusphere-egu2020-10744, 2020.

EGU2020-11695 | Displays | CR5.8

Exploring firn aquifers on the Muller Ice Shelf, Antarctica

Shelley MacDonell, Remi Valois, Francisco Fernandoy, Paula Villar, Gino Casassa, Arno Hammann, and Marcelo Marambio

Over the last two decades, several ice shelves in the Antarctic Peninsula region have experienced significant volume loss or even total collapse driven by atmospheric, oceanic and hydrological processes. Of the three main drivers of ice shelf change, the role of liquid water on and within ice shelves is perhaps the least well defined, largely due to the paucity of field measurements. This study aims to characterise firn aquifers found within an ice shelf vulnerable to hydrological processes. To achieve this objective we use observations collected during two field seasons on the Müller Ice Shelf. The Müller Ice Shelf, the northernmost ice shelf on the western edge of the Antarctic Peninsula, presents a unique opportunity to accomplish our goal: both surface melt pools and subsurface refreezing are known to occur there, and the shelf straddles the -9ºC annual mean isotherm currently considered the limit of ice shelf viability. Measurements from the 2018/19 and 2019/20 field seasons include firn core stratigraphy, geophysical measurements and thermistor datasets, which when combined help to characterise the size and structure of water bodies found within the ice shelf. Whilst during the initial field campaign, no liquid water was observed at the surface, during the drilling of three firn cores liquid water was present at all sites at depths within 20 m of the surface. The prevalence of water and the characterization of the aquifers will provide a baseline for future dynamical studies using physically based models.

How to cite: MacDonell, S., Valois, R., Fernandoy, F., Villar, P., Casassa, G., Hammann, A., and Marambio, M.: Exploring firn aquifers on the Muller Ice Shelf, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11695, https://doi.org/10.5194/egusphere-egu2020-11695, 2020.

Despite the well-researched implications of SGL development and drainage for changes in mass balance and dynamics on Greenland, little is known about the role of energy absorption by lakes on Antarctica. Supraglacial lakes (SGLs) are prevalent features of Antarctic surface hydrology forming mainly on ice shelves (<100 m a.s.l) and efficiently conveying atmospheric energy to the ice interior (Lenaerts et al., 2017; Bell et al., 2018). SGLs on Antarctic Ice Shelves are significant for mass balance given lower surface albedo and drainage-induced collapse of fringing ice shelves and consequent increased discharge from tributary outlet glaciers (Stokes et al., 2019).

There have been few efforts to quantify the energy exchanges between SGLs, atmosphere and ice to calculate their effects on glacier ablation (Law et al., 2018), although Miles et al. (2016) find that ponds on a debris-covered mountain glacier input large amounts of energy to underlying ice. Therefore, it is proposed that ice-sheet ponds also act as a significant energy exchange surface inputting large amounts of energy to the ice.

This study aims to code a computationally efficient surface energy balance model (SEB) in Google Earth Engine Editor to quantify how much extra energy is absorbed by SGLs at the during 2019 melt season. The most prolific surface melt is associated with the Antarctic Peninsula, but several East Antarctic ice shelves experience upwards of 60 days/yr of melting (Bell et al., 2018). Near-grounding line negative mass balance of the Nivlisen Ice Shelf (70 S, 12 E) in central Dronning Maud Land, East Antarctica, is sufficient to form SGLs and will be used to test SEB accuracy.

The one-dimensional numerical energy-balance SGL model GlacierLake, developed by Law et al. (2018), will be implemented in Google Earth Engine to code for surface energy exchanges. GlacierLake is most sensitive to the proportion of shortwave radiation absorbed at the surface which indicates that it is responsive to surface energy fluxes and is useful for the purposes of this study. A variety of methods, including NDWI and Principle Components Analysis, will be evaluated for use to classify lake and slush extents.

Given that it takes 3.4 x 105 J/kg of latent heat to melt ice at 0 °C, the volume of liquid water on the Nivlisen ice shelf implies how much atmospheric energy has been transferred to the ice shelf. The modelled quantification of extra energy absorbed by lakes will be compared to the observed water volume on the Nivlisen Ice Shelf to test model accuracy.

Whilst this study will focus on the Nivlisen Ice Shelf, the SEB model may be applied at pan-Antarctic scales to calculate the ice-sheet wide extra energy absorbed by surface meltwater pooling. A precise quantification of the present impact of energy absorption by lakes on mass balance and dynamics provides a baseline to gauge how meltwater contribution could evolve under atmospheric warming.

How to cite: Lefroy, N. and Arnold, N.: Quantification of the Impact of Supraglacial Lakes and Slush on Surface Energy Balance of Ice Shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20847, https://doi.org/10.5194/egusphere-egu2020-20847, 2020.

In Antarctica, basal melting in the ice-sheet’s interior generates subglacial water that is routed via the subglacial hydrological system towards the margins. At the grounding zone, the subglacial meltwater comes into contact with ocean water subject to tides. The mixing of the two water masses may be one reason for velocities variations on tidal timescales, providing a window into processes of basal sliding. With this goal in mind, we instrumented a flowline across the grounding zone of Priestley glacier, Antarctica, with 4 differential GNSS stations co-located with advanced phase sensitive radars (ApRES) and tiltmeters all measuring continuously over several months. Moreover, we installed a Terrestrial Radar Interferometer (TRI) overlooking the glacier from an adjacent rock outcrop. The to our knowledge first-time deployment of the TRI in Antarctica reveals a stunning picture of grounding-zone dynamics providing spatially coherent 1D flowfields every 3 hours over a time period of 10 days. This enables interpretations of velocity changes measured by GNNS in an unprecedented spatial context. We complement our on-site geophysical dataset with airborne ice-penetrating radar as well as spaceborne InSAR data using timeseries from TanDEM-X, Sentinel-1A, and the ERS satellites.

TRI and GNSS stations jointly detect tidal velocity fluctuations (> 50 % around the mean) which decay landwards with increasing distance from the grounding line. Triple differences in satellite interferometry reveal transient bull’s eye patterns far upstream of the grounding line quantifying localized surface lowering together with adjacent surface uplift. We interpret this as a result from abruptly migrating subglacial water pockets cascading over obstacles in the basal topography. The TRI also shows such bull’s eye patterns pulsating in our highly resolved time series. Moreover, all GNSS stations and the TRI detect a short-lived acceleration event (~100 % horizontal speedup over 2 hours) paired with spatially coherent surface uplift (~15 cm). Magnitude and duration of this event suggests operation of hydraulic jacking, a mechanism explaining short-lived speed-ups with pressure variations in a linked-cavity system. However, usually this is pre-conditioned to the existence of significant surface meltwater entering the subglacial hydrological system, which is not the case at our study site. Our joint observations with multiple sensors and instruments therefore  provide unique observations to further develop our understanding of basal sliding, particularly it's dependency on upstream water supply and ocean tides.

How to cite: Drews, R., Wild, C., Neckel, N., Marsh, O., Rack, W., and Ehlers, T. A.: The heartbeat of a glacier: Cascading subglacial water pockets and ocean tides cause hourly to daily ice-flow variations of Priestley Glacier, Antarctica, detected with Terrestrial Radar Interferometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10743, https://doi.org/10.5194/egusphere-egu2020-10743, 2020.

EGU2020-15968 | Displays | CR5.8

The extreme Greenland melt season of 2019 in a 16-year time series of surface energy balance at the Kangerlussuaq transect

Peter Kuipers Munneke, Carleen Reijmer, Paul Smeets, and Michiel van den Broeke

In 2019, the Kangerlussuaq transect has experienced a record surface melt season at some stations, exceeding even the melt seasons of 2010 and 2012. We demonstrate that net radiation has been driving the high surface melt rates especially in the higher parts of the transect.

Since 2003, continuous measurements of the surface energy budget are made in a transect of four automatic weather stations, spanning the ablation area close to the ice edge to the accumulation are of the Greenland Ice Sheet. All available data have been homogenized and corrected, and an unprecedented time series of surface energy budget is presented here, including meltwater production. In this contribution, the melt season of 2019 is put into the longer-term context, and precise atmospheric drivers of the melt are exposed.

Sixteen years of data clearly reveal the inland and upward expansion of the ablation area. The weather station closest to the equilibrium line (S9) shows a clear and distinct reduction in albedo, and a relatively strong increase in surface melt, which has started to exceed accumulation during the period of observation. Photographs of the area around S9 show that the surface has undergone major changes between 2003 and 2019, now featuring many surface hydrological features that were completely absent in 2003.

These changes have important implications for the hydrology of the surface, the near-surface, and the underlying firn. A firn model calculation reveals that the entire firn column has been heating by several degrees Celsius in the percolation zone, due to refreezing of meltwater. Sudden, stepwise warming is seen in extreme melt seasons like 2019.

How to cite: Kuipers Munneke, P., Reijmer, C., Smeets, P., and van den Broeke, M.: The extreme Greenland melt season of 2019 in a 16-year time series of surface energy balance at the Kangerlussuaq transect, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15968, https://doi.org/10.5194/egusphere-egu2020-15968, 2020.

EGU2020-17968 | Displays | CR5.8

Greenland’s supraglacial lakes increase by a quarter in the last 20 years

James Lea and Stephen Brough

Supraglacial lakes represent a fundamental component of the surface hydrology of the Greenland ice sheet. Understanding the relationship of these lakes with ice sheet surface mass balance, geometry, location, and how this has changed through time also informs how their drainage can impact ice sheet subglacial hydrology and seasonal flow dynamics. However, previous studies of supraglacial lakes have been limited in spatial and/or temporal scale relative to the entire ice sheet.

Here we use the entire MODIS Terra archive within Google Earth Engine to derive maps of supraglacial lake cover every day of every melt season for the last 20 years for the entire Greenland ice sheet. Through generating annual composites of where lakes are observed, we identify that the frequency of lakes has on average increased by 27% from 2000-2019. Lakes are observed to be occurring at higher elevations in all sectors of the ice sheet for 2010-2019 compared to 2000-2009. Output from the regional climate model MAR suggests that in the most recent decade higher numbers of lakes are being formed for a given volume of runoff.

The observation of lakes that can form more easily, further inland and at higher elevations have significant implications for future surface mass balance, and potentially the dynamics of inland regions of the Greenland ice sheet.

How to cite: Lea, J. and Brough, S.: Greenland’s supraglacial lakes increase by a quarter in the last 20 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17968, https://doi.org/10.5194/egusphere-egu2020-17968, 2020.

CR5.9 – Subglacial Environments of Ice Sheets and Glaciers

EGU2020-3176 | Displays | CR5.9

Sub-Ice Sheet Environments in North Victoria Land during the Last Glacial Maximum

Paul C Augustinus, Silvia Frisia, and Andrea Borsato

Subglacial calcite precipitates from Boggs Valley (71o55’S; 161o31’E; elevation 1,160 m asl., Northern Victoria Land, Antarctica), provided the first radiometrically-dated petrographic, geochemical and genomic evidence of thermogenic subglacial drainage events linked to subglacial eruptions during the Last Glacial Maximum (LGM). The crusts consist of two fabrics: i) a dirty (particulate-rich) microsparite, which marks catastrophic subglacial discharges of meltwater and a ii) dark columnar calcite that formed in pockets of basal melt. Synchrotron Radiation-based micro X-Ray fluorescence reveal that the dirty microsparite is S-rich, and embeds particulates characterized by high Manganese (Mn), Yttrium (Y) and Iron (Fe) concentrations. From previous work, we also know that the microsparite layers contain organic compounds, including amino acids, from which we extracted DNA fragments of microorganisms that lived in diverse sub-Antarctic environments (Frisia et al., 2017). The elongated columnar calcites are characterized by the presence of Arsenic (As) associated with low concentrations of  Mn. Both elements suggest local anaerobic, chemolitothrophic metabolism. Columnar calcite becomes increasingly rich in S near the “discharge” layers.  

Our preliminary interpretation is that during the LGM subglacial volcanism was crucial to sustain life in sub-ice sheet refugia by injecting both nutrients and diverse microbes into the basal ecosystem. The otherwise nutrient-poor, anoxic subglacial environment sustained a population of chemolithotrophs, which may have also been “allochthonous”.   

How to cite: Augustinus, P. C., Frisia, S., and Borsato, A.: Sub-Ice Sheet Environments in North Victoria Land during the Last Glacial Maximum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3176, https://doi.org/10.5194/egusphere-egu2020-3176, 2020.

EGU2020-9503 | Displays | CR5.9

Extreme melt season traction variations recorded on the western Greenland Ice Sheet

Nathan Maier, Neil Humphrey, Joel Harper, and Toby Meierbachtol

Basal traction is fundamental to the dynamics of glaciers and ice sheets. On the Greenland Ice Sheet meltwater delivery to the bed and evolving drainage efficiency and connectivity modulate traction producing a characteristic seasonal velocity response. While numerical modelling and basal pressure observations have linked these velocity variations to evolving subglacial drainage, a high-fidelity record of basal traction is needed to constrain the timing and magnitude of traction changes that modulate summer ice flow.  We present a continuous summertime record of basal traction, basal ice deformation, and surface velocity measured at a densely instrumented field site in western Greenland. We use a five-station GPS network and englacial measurements of shearing and ice temperature to directly estimate the basal traction using the force balance method at the site-scale (100s of meters). Localized traction variations (10s of meters) are inferred via variations in the near-basal deformation field recorded by inclinometers installed directly above the basal interface. Combined, the data give a multi-scale perspective on how the basal traction changes during summer and relates to the conceptual model of melt season flow. Our results show the basal traction migrates between extremes during the melt season, with magnitudes greater than three times the average winter traction and near zero. The basal traction extremes correspond with the spring event, the inferred transition to efficient drainage, and the late summer velocity decline. The rapid strengthening and weakening of the basal interface show the complicated interaction of local and regional forcing that modulate melt season sliding. The near-basal deformation variations allow us to constrain the stress configuration and drainage state during each extreme traction period. Overall, the results allow us to refine the conceptual model for melt season traction changes and provide measured estimates of traction variations which can be used as quantitative targets for coupled drainage – ice dynamic models.

How to cite: Maier, N., Humphrey, N., Harper, J., and Meierbachtol, T.: Extreme melt season traction variations recorded on the western Greenland Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9503, https://doi.org/10.5194/egusphere-egu2020-9503, 2020.

EGU2020-10710 | Displays | CR5.9

Investigating Spatio-temporal Changes in Subglacial Hydrology from Dense Array Seismology.

Ugo Nanni, Florent Gimbert, Philippe Roux, and Albanne Lecointre

Subglacial hydrology strongly modulates glacier basal sliding, and thus likely exerts a major control on ice loss and sea-level rise. However, the limited direct and spatialized observations of the subglacial drainage system make difficult to assess the physical processes involved in its development. Recent work shows that detectable seismic noise is generated by subglacial water flow, such that seismic noise analysis may be used to retrieve the physical properties of subglacial channelized water flow. Yet, investigating the spatial organisation of the drainage system (e.g. channels numbers and positions) together with its evolving properties (e.g. pressure conditions) through seismic observations remains to be done. The objective of this study is to bring new insights on the subglacial hydrology spatio-temporal dynamics using dense array seismic observations.

We use 1-month long ground motion records at a hundred of sensors deployed on the Argentière Glacier (French Alps) during the onset of the melt season, when the subglacial drainage system is expected to strongly evolve in response to the rapidly increasing water input. We conduct a multi-method approach based on the analysis of both amplitude and phase maps of seismic signals. We observe characteristic spatial patterns, consistent across those independent approaches, which we attribute to the underlying subglacial drainage system.

The phase-driven approach shows seismic noise sources that focuses in the along-flow direction as the water input increases. We identify this evolution as the development of the main subglacial channel whose position is coherent with the one expected from hydraulic potential calculations. During periods of rapid changes in water input (5 days over 31) and concomitant glacier acceleration the amplitude-driven approach shows spatial pattern highly consistent with the seismic noise sources location. At this time, we suggest that the spatial variations in the amplitude are representative of the water pressure conditions in subglacial channels and surrounding areas. Our spatialized observations therefore reveal the spatio-temporal evolution of the subglacial drainage system together with its changing pressure conditions. We observe, for instance, that channels develop at the very onset of the melt-season and rapidly capture the water from surrounding areas. Such unique observations may allow to better constrain the physics of subglacial water flow and therefore strengthen our knowledge on the dynamics of subglacial environments.

How to cite: Nanni, U., Gimbert, F., Roux, P., and Lecointre, A.: Investigating Spatio-temporal Changes in Subglacial Hydrology from Dense Array Seismology. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10710, https://doi.org/10.5194/egusphere-egu2020-10710, 2020.

EGU2020-18400 | Displays | CR5.9

Hard thermal turbulence in Antarctic Subglacial Lakes

Martin Siegert and Louis-Alexandre Couston

Over 250 stable and isolated subglacial lakes exist at and close to the ice-sheet center in Antarctica. The physical conditions within subglacial lakes, and the differences between distinct lake settings, are critical to evaluating how and where life may best exist. Here, we demonstrate that upward heating by Earth’s geothermal flux provides efficient stirring of Antarctic subglacial lakes’ water, in a variety of ways related to their water depth, ice overburden and ceiling slope. We show that most lakes are in a regime of hard convective turbulence, enabling efficient mixing of nutrient- and oxygen-enriched top melt-water, which is essential for biome formation. Lakes beneath a thin (about less than 3 km) ice cover and lakes with a thick (more than 3 km) ice cover experience similarly-large velocities, but the latter have significantly larger temperature fluctuations and have a stable layer up to several tens of meters thick adjacent to the ice. We discuss the implications of hydrological conditions on the concentration of particulates in the water column.

How to cite: Siegert, M. and Couston, L.-A.: Hard thermal turbulence in Antarctic Subglacial Lakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18400, https://doi.org/10.5194/egusphere-egu2020-18400, 2020.

EGU2020-1173 | Displays | CR5.9

Complex basal conditions influence flow at the onset of the North East Greenland Ice Stream

Steven Franke, Daniela Jansen, John Paden, and Olaf Eisen

The onset and high upstream ice surface velocities of the North East Greenland Ice Stream (NEGIS) are not yet well reproducible in ice sheet models. A major uncertainty remains the understanding of basal sliding and a parameterization of basal conditions. In this study, we assess the slow-flowing part of the NEGIS in a systematic analysis of the basal conditions and investigate the increased ice flow. We analyze the spectral basal roughness in correlation with basal return power from an airborne radar survey with AWIs ultra-wideband radar system in 2018 and compare our results with current ice flow geometry and ice surface flow. We observe a roughness anisotropy where the ice stream widens, indicating a change from a smooth and soft bed to a harder bedrock as well as the evolution of elongated subglacial landforms. In addition, at the upstream part of the NEGIS we find a clear zoning of the bedrock return power, indicating an increased water content at the base of the ice stream. At the downstream part, we observe an increased bedrock return power throughout the entire width of the ice stream and outside its margins, indicating enhanced melting and the distribution of basal water beyond the shear zones.

How to cite: Franke, S., Jansen, D., Paden, J., and Eisen, O.: Complex basal conditions influence flow at the onset of the North East Greenland Ice Stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1173, https://doi.org/10.5194/egusphere-egu2020-1173, 2020.

EGU2020-9431 | Displays | CR5.9

Detecting active subglacial lakes beneath the Greenland Ice Sheet using ArcticDEM

Jade Bowling, Amber Leeson, Malcolm McMillan, Stephen Livingstone, and Andrew Sole

A total of 63 subglacial lakes have been documented beneath the Greenland Ice Sheet using a combination of radio-echo sounding and surface elevation change measurements. Of these, only 7 lakes have shown evidence of hydrological activity over the period 2001-2018. Draining lakes have been observed to drive transient changes in local ice flow speeds in Antarctica. The sudden discharge of water during a subglacial lake outburst event causes the subglacial lake roof to subside, which propagates to the surface, resulting in the formation of collapse basins (typically ~50-70 m in depth). These surface features can be detected using remote sensing techniques.

Whilst over 100 active subglacial lakes have been identified in Antarctica, predominantly beneath ice streams, little is known about the extent, volume of water stored and residence times of active subglacial lakes in Greenland, together with any potential influence of drainage events on local ice dynamics and sediment evacuation rates. Here, we explore the potential of the high resolution ArcticDEM stereogrammetric digital surface model (DSM) open source dataset, generated from satellite optical imagery, to identify and monitor subglacial lake-derived collapse basins. The ArcticDEM provides 2 m time-stamped surface elevation data, covering ~160 million km2, offering an exciting opportunity to map elevation changes between 2009-2017. This study presents the first effort to utilise ArcticDEM data at an ice-sheet scale to identify and monitor active subglacial lakes beneath the Greenland Ice Sheet, which we hope will ultimately improve our understanding of its complex subglacial hydrological system.

How to cite: Bowling, J., Leeson, A., McMillan, M., Livingstone, S., and Sole, A.: Detecting active subglacial lakes beneath the Greenland Ice Sheet using ArcticDEM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9431, https://doi.org/10.5194/egusphere-egu2020-9431, 2020.

EGU2020-10204 | Displays | CR5.9

Cryoegg: development and field trials of a wireless subglacial probe for deep, fast-moving ice

Michael Prior-Jones, Elizabeth Bagshaw, Jonathan Lees, Lindsay Clare, Stephen Burrow, Jemma Wadham, Mauro A Werder, Nanna B Karlsson, Dorthe Dahl-Jensen, Poul Christoffersen, and Bryn Hubbard

Innovative technological solutions are required to access and observe subglacial hydrological systems beneath glaciers and ice sheets. Wireless sensing systems can be used to collect and return data without the risk of losing data from cable breakage, which is a major obstacle when studying fast flowing glaciers and other high-strain environments. However, the performance of wireless sensors in deep and fast-moving ice has yet to be evaluated formally. We report experimental results from Cryoegg: a spherical probe that can be deployed along an ice borehole and either remain fixed in place or potentially travel through the subglacial hydrological system. The probe makes measurements in-situ and sends them back to the surface via a wireless link. Cryoegg uses very high frequency (VHF) radio to transmit data through up to 1.3 km of cold ice to a surface receiving array. It measures temperature, pressure and electrical conductivity, returning all data in real time. This transmission uses Wireless M-Bus on 169 MHz; we present a simple “radio link budget” model for its performance in cold ice and confirm its validity experimentally. Power is supplied by an internal battery with sufficient capacity for two measurements per day for up to a year, although higher reporting rates are available at the expense of battery life. Field trials were conducted in 2019 at two locations in Greenland (the EastGRIP borehole and the RESPONDER project site on Sermeq Kujalleq/Store Glacier) and on the Rhone Glacier in Switzerland.  Our results from the field demonstrate Cryoegg’s utility in studying englacial channels and moulins, including estimating moulin discharge through salt dilution gauging with the instrument deployed deep within the moulin. Future iterations of the radio system will allow Cryoegg to transmit through up to 2.5 km of ice.

How to cite: Prior-Jones, M., Bagshaw, E., Lees, J., Clare, L., Burrow, S., Wadham, J., Werder, M. A., Karlsson, N. B., Dahl-Jensen, D., Christoffersen, P., and Hubbard, B.: Cryoegg: development and field trials of a wireless subglacial probe for deep, fast-moving ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10204, https://doi.org/10.5194/egusphere-egu2020-10204, 2020.

Deep-water ‘stable’ subglacial lakes likely contain microbial life adapted in isolation to extreme environmental conditions. How water is supplied into a subglacial lake, and how water outflows, is important for understanding these conditions. Isochronal radio-echo layers have been used to infer where melting occurs above Lake Vostok and Lake Concordia in East Antarctica but have not been used more widely. We examine englacial layers above and around Lake Ellsworth, West Antarctica, to establish where the ice sheet is ‘drawn down’ towards the bed and, thus, experiences melting. Layer drawdown is focused over and around the NW parts of the lake as ice, flowing obliquely to the lake axis, becomes afloat. Drawdown can be explained by a combination of basal melting and the Weertman effect, at the transition from grounded to floating ice. We evaluate the importance of these processes on englacial layering over Lake Ellsworth and discuss implications for water circulation and sediment deposition. We report evidence of a second subglacial lake near the head of the hydrological catchment and present a new high-resolution bed DEM and hydropotential model of the lake outlet zone. These observations provide insight into the connectivity between Lake Ellsworth and the wider subglacial hydrological system.

How to cite: Ross, N. and Siegert, M.: Basal melting over Subglacial Lake Ellsworth and its catchment: insights from englacial layering, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2885, https://doi.org/10.5194/egusphere-egu2020-2885, 2020.

EGU2020-5858 | Displays | CR5.9

The influence of sliding velocity and effective stress on the distribution of strain in subglacial till

Dougal Hansen, Anders Daamsgard, and Lucas Zoet

The distribution of strain in actively deforming subglacial till is an important control on the sliding velocity and sediment transport of soft-bedded glaciers. In situ field observations, laboratory experiments, and numerical simulations have demonstrated that strain accumulation within subglacial till is often greatest at the ice-bed interface and decreases monotonically with depth, forming a convex-upward profile. However, the mechanisms that set the form of the profile and depth of deformation remain unconstrained. Here we systematically test the influence of two independent variables, effective stress and sliding velocity, on the distribution of strain in a fine-grained, sandy till emplaced beneath a layer of moving ice. Laboratory sliding experiments, conducted with a brand-new ring-shear device with a transparent sample chamber, are coupled with two suites of state-of-the-art numerical experiments using 1) a discrete element model and 2) a non-local granular fluidity continuum model designed to emulate till deformation. Five effective stresses and five sliding velocities are tested with the other parameter held constant (velocity and effective stress, respectively). For the ring shear experiments, images of the till bed are acquired at regular intervals, and we quantify the displacement of sediment grains that occurs between image captures using digital image correlation. These experiments represent the first instance where the deformation of till during glacier slip can be observed in real-time and linked directly to its controlling processes. Furthermore, they provide an opportunity to juxtapose the predictions of two new granular dynamic models against empirical observations in a controlled setting, providing an invaluable ground truth for future, larger-scale implementations simulating bedform genesis and soft-bedded glacier dynamics.

How to cite: Hansen, D., Daamsgard, A., and Zoet, L.: The influence of sliding velocity and effective stress on the distribution of strain in subglacial till, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5858, https://doi.org/10.5194/egusphere-egu2020-5858, 2020.

EGU2020-5861 | Displays | CR5.9

Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

Emma Lewington, Stephen Livingstone, Chris Clark, Andrew Sole, and Robert Storrar

Despite being widely studied, subglacial meltwater landforms are typically mapped and investigated individually, thus the drainage system as a whole remains poorly understood. Here, we identify and map all visible traces of subglacial meltwater flow across the Keewatin sector of the former Laurentide Ice Sheet from the ArcticDEM, generating significant new insights into the connectedness of the drainage system.

Due to similarities in spacing, morphometry and spatial location, we suggest that the 100s-1000s m wide features often flanking and connecting sections of eskers (i.e. tunnel valleys, meltwater tracks and esker splays) are varying expressions of the same phenomena and collectively term these features ‘meltwater corridors’. Based on observations from contemporary ice masses, we propose a new formation model based on the pressure fluctuations surrounding a central conduit, in which the esker records the imprint of the central conduit and the wider meltwater corridors the interactions with the surrounding distributed drainage system, or variable pressure axis (VPA).

We suggest that the widespread aerial coverage of meltwater corridors across the Keewatin sector provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuation and variations in spatial distribution and evolution of the subglacial drainage system, which have important implications for ice sheet dynamics. 

How to cite: Lewington, E., Livingstone, S., Clark, C., Sole, A., and Storrar, R.: Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5861, https://doi.org/10.5194/egusphere-egu2020-5861, 2020.

EGU2020-7185 | Displays | CR5.9

Basal conditions of Kongsvegen at the onset of surge - revealed using seismic vibroseis surveys

Emma C. Smith, Anja Diez, Olaf Eisen, Coen Hofstede, and Jack Kohler

Kongsvegen is a well-studied surge-type glacier in the Kongsfjord area of northwest Svalbard. Long-term monitoring has shown that the ice surface velocity has been increasing since around 2014; presenting a unique opportunity to study the internal ice structure, basal conditions and thermal regime, all of which play a crucial role in initiating glacier surges. In April 2019, three-component seismic vibroseis surveys were conducted at two sites on the glacier, using a small Electrodynamic Vibrator source (ElViS). The first site is in the ablation area and the second near the equilibrium line, where the greatest increase in ice-surface velocity has been observed.

Initial analysis indicates the conditions at the two sites are significantly different. At the ablation area site, the ice is around 220 m thick, and the bed is relatively flat and unvaried, with no clear change in the bed reflection along the profile. The bed appears to comprise a uniform and undisturbed sediment package ~60 m thick, and there are no clear englacial reflections within the ice column. By contrast at the second site, the ice is around 390 m thick, and the internal ice structure is much more complex. Clear internal ice reflections are visible at depths between 150-250 m, and further reflections in the 100 m above the bed indicate there could be shearing or sediment entrainment in this area. Below the bed, cross-cutting layers are clearly visible and the bed reflection itself shows changing reflection polarity – suggesting water or very wet sediment is present in some areas.  The contrast between these two sites at the onset of a surge phase allows us to investigate the physical conditions that are conducive to surge initiation, both at the ice-bed interface and within the ice column.

How to cite: Smith, E. C., Diez, A., Eisen, O., Hofstede, C., and Kohler, J.: Basal conditions of Kongsvegen at the onset of surge - revealed using seismic vibroseis surveys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7185, https://doi.org/10.5194/egusphere-egu2020-7185, 2020.

EGU2020-10035 | Displays | CR5.9

Inferring controls on basal drag in the Amundsen Sea sector of Antarctica

Robert Arthern, Rosie Williams, Kelly Hogan, Alex Brisbourne, Andrew Smith, and Tom Jordan

We consider a variety of ways that the basal drag that acts to resist the sliding of an ice sheet can be inferred from satellite observations, or from in situ observations. Three approaches are considered here. (1) use of inverse methods combined with large scale models of ice flow. (2) spectral analysis of basal topography combined with a theory of ice flow near small scale undulations, and (3) seismic methods that probe the physical characteristics of the subglacial sediment. Consideration is given to which sliding relationships are consistent with the available observations, and to identifying measurements that could help reduce ambiguity in sliding laws.

How to cite: Arthern, R., Williams, R., Hogan, K., Brisbourne, A., Smith, A., and Jordan, T.: Inferring controls on basal drag in the Amundsen Sea sector of Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10035, https://doi.org/10.5194/egusphere-egu2020-10035, 2020.

EGU2020-13260 | Displays | CR5.9

The meltwater feedbacks on ice dynamics, elevation versus lubrication

Basile de Fleurian, Petra Langebroek, and Paul Halas

In recent years, temperatures over the Greenland ice sheet have been rising leading to an increase in surface melt.  Projections show that this augmentation of surface melt will continue in the future and spread to higher elevations. As it increases, melt leads to two different feedbacks on the dynamic of the Greenland ice sheet. This augmentation of melt lowers the ice surface and changes its overall geometry hence impacting the ice dynamics through ice deformation. The other feedback comes into play at the base of glaciers. Here, the increase of water availability will impact the distribution of water pressure at the base of glaciers and hence their sliding velocity. The first feedback is relatively well known and relies on our knowledge of the rheology and deformation of ice. The lubrication feedback acting at the bed of glaciers is however highly uncertain on time scales longer than a season. Here we apply the  Ice  Sheet  System  Model  (ISSM)  to  a  synthetic  glacier  which  geometry  is  similar to the one of a Greenland ice sheet land terminating glacier. The dynamic contributions from ice deformation and sliding are separated to study their relative evolution. This is permitted by the use of a dynamical subglacial hydrology model that allows to link the basal sliding to the meltwater production through an appropriate friction law. The  model  is  forced  through  a  simple  temperature  distribution  and  a  Positive  Degree  Day  model which allows to apply a large range of different forcing scenarios. Of particular interest is the evolution of the distribution of the efficient and inefficient component of the subglacial drainage system and their different response to the distribution of melt during the year which directly impact the sliding regime at the base of the glacier.

How to cite: de Fleurian, B., Langebroek, P., and Halas, P.: The meltwater feedbacks on ice dynamics, elevation versus lubrication, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13260, https://doi.org/10.5194/egusphere-egu2020-13260, 2020.

EGU2020-17484 | Displays | CR5.9

Subglacial Drainage Routes of the Last Scandinavian Ice Sheet

Nico Dewald, Chris D. Clark, Stephen J. Livingstone, Jeremy C. Ely, and Anna L.C. Hughes

The configuration of subglacial drainage systems has a major impact on the dynamics of ice sheets. However, the logistical challenges of measuring subglacial processes beneath contemporary ice sheets hinder our understanding about the spatio-temporal evolution of subglacial drainage systems. Furthermore, today’s observations on contemporary ice sheets are inherently limited to a short period within the process of deglaciation. Landforms generated by the flow of meltwater at the ice-bed interface offer the potential to study both large-scale (103-106 km2) and long-term (103-105 a) developments of subglacial drainage networks beneath past ice sheets. Despite collectively recording subglacial drainage, individual meltwater landform types such as eskers, meltwater channels and tunnel valleys, and hummock corridors have mostly been considered as separate entities. Using high-resolution (1-2 m) DEMs, we summarise the suite of interconnected subglacial meltwater landforms into a common drainage signature herein called a subglacial drainage route. Our integrated map of subglacial meltwater landforms presents the large-scale distribution of major subglacial drainage routes across Scandinavia and provides a basis for future research about the long-term evolution of subglacial drainage networks and its effect on ice dynamics of the Scandinavian Ice Sheet.

How to cite: Dewald, N., Clark, C. D., Livingstone, S. J., Ely, J. C., and Hughes, A. L. C.: Subglacial Drainage Routes of the Last Scandinavian Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17484, https://doi.org/10.5194/egusphere-egu2020-17484, 2020.

EGU2020-6042 | Displays | CR5.9

Constraints on glacier bedrock roughness from spectral analysis of glacier forefields

Jacob Woodard, Lucas Zoet, Neal Iverson, and Christian Helanow

The slip of hard bedded glaciers partly depends on the morphology of their beds. Thus, constraints on subglacial bedrock morphology are imperative for accurate forecasting of glacier flow rates. Digital elevation models (DEMs) from ten valley glacier and ice-sheet forefields were used to analyze the spectral patterns of recently deglaciated bedrock. Valley glacier DEM length scales are 0.1 m - 100 m, while ice sheet DEM length scales are 10 m -1000 m. We observe a higher spectral roughness and aspect ratio (i.e. bump height/wavelength) for valley glaciers than ice-sheet forefields. However, forefield aspect ratios span a narrow range and decrease with increasing length scale at a consistent rate despite a range of bedrock lithologies analyzed. This implies that bedrock shear strength (τ) scales with length scale (L), as τ ~ L-0.37, closely matching the bulk strength scaling relation seen in fault rocks (Brodsky et al., 2016). These morphological constraints of forefields allow extrapolation of bedrock roughness beneath active glaciers that can help predict sliding rates.

How to cite: Woodard, J., Zoet, L., Iverson, N., and Helanow, C.: Constraints on glacier bedrock roughness from spectral analysis of glacier forefields , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6042, https://doi.org/10.5194/egusphere-egu2020-6042, 2020.

EGU2020-6941 | Displays | CR5.9

Evidence of uplift at Argentière glacier (Mont Blanc area, France)

Christian Vincent, Andrea Walpersdorf, Adrien Gilbert, Olivier Gagliardini, Florent Gimbert, Fabien Gillet-Chaulet, Luc Piard, Bruno Jourdain, Diego Cusicanqui, Luc Moreau, Olivier Laarman, and Delphine Six

Understanding basal processes is a prerequisite for predicting the overall motion of glaciers and its response to climate change. Although a number of studies have shown that subglacial hydrology affects glacier’s basal sliding motion, the involved mechanisms remain poorly known. Several studies suggested that glacier velocity increases with englacial and subglacial water storage, but observational quantification of subglacial water storage and associated velocity changes are challenging to make due to uncertainties on velocity measurements and on vertical straining.

Here we tackle this observational challenge through analyzing numerous field measurements from the surface and from the subglacial observatory on the Argentière Glacier (French Alps). We analyze specifically the relationships between daily sliding velocities (measured continuously at the glacier base), surface horizontal and vertical velocities from DGPS observations and ice thickness changes over years 2018 and 2019. We find strong upward surface movements of about 0.5 m during the winter until the beginning of May that cannot be explained by longitudinal strain rate changes. We support that it is caused by water volume increase in subglacial cavities.

Further analyzing the relationships between cavity growth, sliding and surface velocities, we find that unlike in previous studies bed separation variations are not synchronous with sliding speed variations. Surface uplift starts in winter, which is long before the spring sliding acceleration, and surface drop occurs mid-summer, which is long before the end of summer sliding deceleration. These findings support that the link between subglacial water storage and sliding speed may not be as direct as previously thought.

How to cite: Vincent, C., Walpersdorf, A., Gilbert, A., Gagliardini, O., Gimbert, F., Gillet-Chaulet, F., Piard, L., Jourdain, B., Cusicanqui, D., Moreau, L., Laarman, O., and Six, D.: Evidence of uplift at Argentière glacier (Mont Blanc area, France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6941, https://doi.org/10.5194/egusphere-egu2020-6941, 2020.

EGU2020-6949 | Displays | CR5.9

Linking glacier surface changes to subglacial conduit locations for a temperate Alpine glacier

Pascal Egli, Bruno Belotti, Martino Sala, Stuart Lane, and James Irving

It is well understood that topography near the snout of an alpine glacier may evolve quickly due to differential melting depending on exposure to solar radiation and on debris cover thickness. However, the positioning and shape of subglacial conduits underneath shallow ice may also have an important influence on ice creep and thereby on the topography of this region. This relationship could potentially be used to determine locations of subglacial conduits via the detailed observation of glacier surface changes.

We monitored the ice-marginal zone of the Otemma Glacier in the south-western Swiss Alps with daily UAV surveys at high spatial resolution and with a network of ablation stakes over a period of three weeks. After subtraction of melt measured with ablation stakes, we produced maps of changes in ice surface topography that are due to processes other than melt. In two consecutive summers we conducted three-dimensional GPR surveys in the same area of interest. By looking at these spatially dense grids of GPR measurements, we are able to identify the locations and shape of sub-glacial conduits underneath the ice marginal glacier tongue, for ice thicknesses between 20 m and 50 m. Superposition of the GPR-derived channel maps with those showing the topographic changes suggest a correlation between ice surface changes and processes operating at the glacier bed.

How to cite: Egli, P., Belotti, B., Sala, M., Lane, S., and Irving, J.: Linking glacier surface changes to subglacial conduit locations for a temperate Alpine glacier , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6949, https://doi.org/10.5194/egusphere-egu2020-6949, 2020.

EGU2020-7271 | Displays | CR5.9

Subglacial water pressure records from a fast-flowing outlet glacier in Greenland

Samuel Doyle, Bryn Hubbard, Poul Christoffersen, Marion Bougamont, Robert Law, Tom Chudley, Mike Prior-Jones, and Charlotte Schoonman

Glacier motion is resisted by basal traction that can be reduced significantly by pressurised water at the ice-bed interface. Few records of subglacial water pressure have been collected from fast-flowing, marine-terminating glaciers despite such glaciers accounting for approximately half of total ice discharge from the Greenland Ice Sheet.  The paucity of such measurements is due to the practical challenges in drilling and instrumenting boreholes to the bed, in areas that are often heavily-crevassed, through rapidly-deforming ice that ruptures sensor cables within weeks. Here, we present pressure records and drilling observations from two sites located 30 km from the calving front of Store Glacier in West Greenland, where ice flow averages ~600 m yr-1.  In 2018, boreholes were drilled 950 m to the bed near the margin of a large, rapidly-draining supraglacial lake. In 2019, multiple boreholes were drilled ~1030 m to the bed in the centre of the drained supraglacial lake, and in close proximity to a large, active moulin. All boreholes drained rapidly when they intersected or approached the ice-bed interface, which is commonly interpreted as indicating connection to an active subglacial drainage system. Neighbouring boreholes responded to the breakthrough of subsequent boreholes demonstrating hydrological or mechanical inter-connection over a distance of ~70 m. Differences in the time series of water pressure indicate that each borehole intersected a distinct component of the subglacial hydrological system. Boreholes located within 250 m of the moulin reveal clear diurnal cycles either in phase or anti-phase with moulin discharge. Pressure records from boreholes located on the lake margin, however, show smaller amplitude, and less distinct, diurnal cycles superimposed on longer-period (e.g. multiday) variability. We compare these datasets to those in the literature and investigate consistencies and inconsistencies with glacio-hydrological theory.

How to cite: Doyle, S., Hubbard, B., Christoffersen, P., Bougamont, M., Law, R., Chudley, T., Prior-Jones, M., and Schoonman, C.: Subglacial water pressure records from a fast-flowing outlet glacier in Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7271, https://doi.org/10.5194/egusphere-egu2020-7271, 2020.

EGU2020-7644 | Displays | CR5.9

3D imaging of subglacial lineations under the Rutford Ice Stream, West Antarctica

Rebecca Schlegel, Adam Booth, Tavi Murray, Andy Smith, Alex Brisbourne, Ed King, Roger Clark, and Steph Cornford

There are numerous theoretical descriptions of the subglacial conditions (water availability, subglacial geology, flow dynamics) required for the formation of subglacial lineations, such as mega-scale glacial lineations and drumlins, that are known to be indicative of fast ice flow. Traditionally, mapping in de-glaciated areas, both onshore and offshore, has been undertaken using bathymetric maps, satellite data and field observations; here, lineations currently beneath the Rutford Ice Stream (West Antarctica) have been mapped using ground-penetrating radar (GPR) and seismic methods.

The Rutford Ice Stream is more than 2 km thick, of which 1.4 km are located below sea level. The ice surface speed at the grounding line is >1 m per day, and satellite observations indicate a stable ice flow over the past 30 years. The ice-bed interface is assumed to be at the pressure-melting point, while the bed can be divided into a region of soft, deforming sediment, and one of stiff, non-deforming, sediment. Long, elongated lineations, up to ~14 km, up to 150 m high, and 50-500 m wide, are found aligned in the ice-flow direction in the area of the soft sediment, within which the deposition of a drumlin was observed over a period of <10 years. Together with local erosion occurring in the same timescale, this demonstrates the temporal variability of ice stream beds.

To study the detailed architecture of the lineations, 3D grids of GPR data were acquired during the Antarctic Summer Season 2017/18, enabling 3D-processing and imaging of lineations. Using this unique dataset, in conjunction with previous publications plus data from the paleo record, we hope to better understand the possible mechanisms of formation of subglacial lineations as well as subglacial conditions at the Rutford Ice Stream.

How to cite: Schlegel, R., Booth, A., Murray, T., Smith, A., Brisbourne, A., King, E., Clark, R., and Cornford, S.: 3D imaging of subglacial lineations under the Rutford Ice Stream, West Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7644, https://doi.org/10.5194/egusphere-egu2020-7644, 2020.

EGU2020-8088 | Displays | CR5.9

Glacier surges initiated in the ablation zone of Hagen Brae, Greenland: observations and theory

Douglas Benn, Ian Hewitt, Nanna Karlsson, and Anne Solgaard

Enthalpy balance theory predicts that dynamic oscillations (surge cycles) occur when glaciers cannot achieve stable steady states with regard to their mass and basal enthalpy (heat and water) budgets. That is, if the enthalpy produced by geothermal and frictional heat cannot be removed by conduction or water flux from the bed, sliding-heating feedbacks will lead to surging behaviour. To date, model simulations have focused on 'classic' surges, in which snow accumulation causes ice thickening in a reservoir zone during quiescence, and transition to surge occurs in response to a locally-driven sliding-heating feedbacks. However, many surges are initiated in glacier ablation zones, where surface mass balance is negative. Here, we show that such surges can be explained if the local mass and enthalpy budget is supplemented by non-local sources. Ice thickening during quiescence can occur if ice flux from upglacier exceeds losses by surface melt, and transition to surge occurs if accumulation of water from both local and non-local sources triggers the sliding-heating feedback. We illustrate these processes using data from Hagen Bræ, a major marine terminating glacier in North Greenland. The dataset, which covers the past 35 years at high temporal resolution, shows elevation changes, ice velocities and basal enthalpy budgets over recent surge cycles that are consistent with theory. The average surge cycle lasts 20-30 years while the duration of the active phase is approximately a decade based on the recent cycle. The theory has potentially wide applicability to surges in a range of climatic and topographic contexts.

How to cite: Benn, D., Hewitt, I., Karlsson, N., and Solgaard, A.: Glacier surges initiated in the ablation zone of Hagen Brae, Greenland: observations and theory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8088, https://doi.org/10.5194/egusphere-egu2020-8088, 2020.

EGU2020-9927 | Displays | CR5.9

Repeat Subglacial Lake Drainage and Filling Beneath Thwaites Glacier, West-Antarctic Ice Sheet

George Malczyk, Daniel Goldberg, Noel Gourmelen, Jan Wuite, and Thomas Nagler

Active subglacial lakes have been identified throughout Antarctica, offering a window into subglacial environments and into controls on ice dynamics. Between June 2013 and January 2014 a system of connected subglacial lakes drained in unison under the Thwaites glacier in the West Antarctic ice sheet, the first time that such a system has been observed in the Amundsen Sea Sector. Estimates based on catchment scale melt production suggested that lake drainages of this type should occur every 20 to 80 years. We collected elevations from January 2011 to December 2019 over the Thwaites lake region using the CryoSat-2 swath interferometric mode and ICEsat-2 land ice elevations, as well as ice velocity from the Sentinel-1 SAR mission since 2014. Using various elevation time series approaches, we obtain time dependent elevations over each lake. Results indicate that the upstream lakes undertake a second episode of drainage during mid-2017, only 3 years after the previous event, and that a new lake drained. Unlike the 2013-2014 episode, this new drainage episode contributed to filling one of the downstream lake with no evidence of further downstream activity. This new sub-glacial lake activity under Thwaites offer the possibility to explore lake connectivity, subglacial melt production and the interaction with ice dynamics.

How to cite: Malczyk, G., Goldberg, D., Gourmelen, N., Wuite, J., and Nagler, T.: Repeat Subglacial Lake Drainage and Filling Beneath Thwaites Glacier, West-Antarctic Ice Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9927, https://doi.org/10.5194/egusphere-egu2020-9927, 2020.

EGU2020-12364 | Displays | CR5.9

A slip law for glaciers on deformable beds

Lucas Zoet and Neal Iverson

Slip of marine-terminating ice streams over beds of deformable till is responsible for most of the contribution of the West Antarctic Ice Sheet to sea-level rise. Flow models of the ice sheet and till-bedded glaciers elsewhere require a law that relates slip resistance, slip velocity, and water pressure at the bed. We present results of the first experiments in which pressurized ice at its melting temperature is slid of over a water-saturated till bed. Steady-state slip resistance increases with slip velocity owing to sliding of ice across the bed, but above a threshold velocity till shears at its rate-independent, Coulomb strength. These results motivate a generalized slip law for glacier-flow models that combines processes of hard-bedded sliding and bed deformation.

How to cite: Zoet, L. and Iverson, N.: A slip law for glaciers on deformable beds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12364, https://doi.org/10.5194/egusphere-egu2020-12364, 2020.

EGU2020-17749 | Displays | CR5.9

The development of a subglacial lake monitored with radio echo sounding and comparison with water volumes released during jökulhlaups: Case study from the Eastern Skaftá Cauldron in the Vatnajökull ice cap, Iceland

Eyjolfur Magnusson, Finnur Pálsson, Magnús T. Gudmundsson, Thórdís Högnadóttir, Christian Rossi, Thorsteinn Thorsteinsson, and Erik Sturkel

We present a 6 year record of repeated radio echo sounding (RES) on a profile grid (200-400 m between profiles) surveyed over the Eastern Skaftá Cauldron (ESC). ESC is an ice cauldron produced and maintained by powerful geothermal activity (~1 GW) at the glacier bed. Beneath the cauldron and 200-400 m of ice, water accumulates in a lake and is regularly released in jökulhlaups. The maximum discharge in the river Skaftá exceeded 3000 m3 s-1 in the most recent ones in 2015 and 2018. The record starts in 2014 and consists of annual measurements, obtained in June each year; the last on June 2019. Comparison of the repeated RES profiles (2D migrated) reveals the margin of the lake at different times and enables a classifying of traced reflections into lake and bedrock measurements. The bedrock measurements were obtained with the lake close to its minimum size in 2016, 2017 and 2019 (£~1 km2 compared to 4.0 km2 in 2015), hence it is possible to obtain fairly accurate digital elevation model (DEM) of the glacier/lake bed. This DEM is further constrained by two borehole measurements of the lake bed elevation at its centre. The traced lake reflections and comparison with the bedrock DEM enables creation of a lake thickness maps and an estimate of the lake volume for each survey. The lake thickness maps and volumes in June 2015 and 2018 are compared with the surface lowering pattern and water volumes drained in the jökulhlaups in October 2015 and August 2018. The drained water volume was derived by integrating the surface lowering during the jökulhlaups and adding estimated volume of crevasses formed in the events. The lowering in the 2015 jökulhlaup was obtained from TanDEM-X DEMs of September 23rd and October 10th, shortly before and after the jökulhlaup. The lowering in the 2018 jökulhlaup was derived from dense set of airborne altimetry profiles acquired on August 9th, a few days after the jökulhlaup, compared with a DEM in June 2018 (ArcticDEM in July 2017 corrected with dense GNSS profiles in June 2018). The lake volume estimate from the RES data is 240x106 m3 in June 2015 but 320±20x106 m3 drained from the cauldron in October. In June 2018 a relatively dense RES profile grid (~200 m between profiles) reveals a lake volume of 180x106 m3 while 210±30x106 m3 drained from the cauldron in August. This comparison demonstrates the applicability of our survey approach to monitor the water accumulation in the lake and thus better constrain potential hazard in jökulhlaups.

How to cite: Magnusson, E., Pálsson, F., Gudmundsson, M. T., Högnadóttir, T., Rossi, C., Thorsteinsson, T., and Sturkel, E.: The development of a subglacial lake monitored with radio echo sounding and comparison with water volumes released during jökulhlaups: Case study from the Eastern Skaftá Cauldron in the Vatnajökull ice cap, Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17749, https://doi.org/10.5194/egusphere-egu2020-17749, 2020.

EGU2020-5835 | Displays | CR5.9

3D surface velocity variations of the Argentière glacier (French Alps) monitored with a high resolution continuous GNSS network

Andrea Walpersdorf, Christian Vincent, Florent Gimbert, Agnès Helmstetter, Luc Moreau, Delphine Six, Stéphane Garambois, Laurent Ott, Stéphane Mercier, Olivier Laarman, Luc Piard, Ugo Nanni, Marguerite Mathey, Benoit Urruty, Christian Sue, Jean-Noël Bouvier, Martin Champon, Olivier Romeyer, Jean-Louis Mugnier, and Mathilde Radiguet and the SAUSSURE GNSS team

Five continuous GNSS stations monitor the Argentière glacier surface motion on a longitudinal profile at 2400 m altitude over a full melt season, from April to November 2019. High precision data analysis is enabled by a close-by reference station on the bedrock. This GNSS survey is part of the SAUSSURE project 2019-2022 that aims at increasing our knowledge on the physics of glacier basal sliding, by improving friction laws and validating them in a natural environment. The Argentière glacier is particularly interesting due to its long-term subglacial observatory measuring basal sliding velocity and subglacial discharge. The SAUSSURE project furthermore includes seismic, tiltmeter and piezometer measurements. The bedrock topography is obtained from a Ground Penetrating Radar.

The dense GNSS station setup permits to validate individual antenna movements. We then retrieve horizontal and vertical surface velocities on daily and sub-daily time scales. We can deduce strain rates in between the stations and their evolution in time, and relate this observable with the vertical surface motions. The confrontation of the GNSS data with independent observations allows analyzing the surface motions searching for glacier surges that combine horizontal speed-ups combined with uplift due to bed separation of the ice sheet. These events could give indications about cavity growth in spring. We will also try to investigate sub-daily motions that seem to occur in daily cycles in summer, as hinted at by the basal sliding measurements. These daily cycles are usually also seen in the seismic activity. The phase of the different features varies with respect to the daily cycles of temperature and sub-glacial water pressure. These phase offsets can give us indices on eventual mechanisms of sliding at the bedrock interface. The GNSS measurements represent a rare in situ data set that can contribute to better apprehend mechanisms of basal sliding and to provide high-resolution 3D constraints on physical models of glacier flow.

How to cite: Walpersdorf, A., Vincent, C., Gimbert, F., Helmstetter, A., Moreau, L., Six, D., Garambois, S., Ott, L., Mercier, S., Laarman, O., Piard, L., Nanni, U., Mathey, M., Urruty, B., Sue, C., Bouvier, J.-N., Champon, M., Romeyer, O., Mugnier, J.-L., and Radiguet, M. and the SAUSSURE GNSS team: 3D surface velocity variations of the Argentière glacier (French Alps) monitored with a high resolution continuous GNSS network , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5835, https://doi.org/10.5194/egusphere-egu2020-5835, 2020.

EGU2020-10537 | Displays | CR5.9

Geomorphology, distribution and composition of subglacial triangular hummocks (murtoos) in Sweden and Finland

Mark Johnson, Joni Mäkinen, Gustaf Peterson, Antti Ojala, Christian Öhrling, Elina Ahokangas, Izabella Remmert, Karu Kajuutti, and Jukka-Pekka Palmu

Triangular hummocks of subglacial origin have been identified in Sweden and Finland due to the increased resolution provided by LiDAR imagery. Their triangular shape is distinctive and recognizable as clearly identifiable landforms. These forms have been previously mapped in some cases as dead-ice hummocks, but geomorphic relationships with eskers, flutes ribbed moraine and De Geer moraines show these to be subglacial. We refer to these new landforms as ‘murtoos.’ Morphometric measurements show murtoos to be 50 to 200 m long and 50 to 100 m wide. The orientation of their apices strongly correlates with local ice-flow orientation. They form preferentially on beds that slope down-ice.  In many cases, they occur in patches in an ice-flow parallel path with eskers, defining corridors we believe to be of subglacial meltwater origin. Murtoos are composed primarily of heterogeneous diamicton with variable amounts of bedded sand and gravel. Murtoos are most common where glacier-melt rates were high during deglaciation (Bølling-Allerød and Holocene), and they are absent where extensive frozen-bed conditions were present. We suggest murtoos are a landform produced as a glacier-bed adjustment to increased delivery of supraglacial meltwater during deglaciation.

How to cite: Johnson, M., Mäkinen, J., Peterson, G., Ojala, A., Öhrling, C., Ahokangas, E., Remmert, I., Kajuutti, K., and Palmu, J.-P.: Geomorphology, distribution and composition of subglacial triangular hummocks (murtoos) in Sweden and Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10537, https://doi.org/10.5194/egusphere-egu2020-10537, 2020.

CR6.2 – Rapid changes in sea ice: processes and implications

EGU2020-897 | Displays | CR6.2

Seasonal transitions of Arctic sea ice over the satellite era in CMIP6 models

Abigail Smith, Alexandra Jahn, and Muyin Wang

Projections of Arctic sea ice area show substantial model spread in CMIP3, CMIP5 and early results from CMIP6. Here we assess how simulated seasonal transitions in Arctic sea ice may be contributing to the large inter-model spread. For this we make use of CMIP6 models, the CESM Large Ensemble and the new Arctic Sea Ice Seasonal Change and Melt/Freeze Climate Indicators satellite dataset. Spring ice loss and fall ice growth can be characterized by various metrics (melt onset, break-up, opening, freeze onset, freeze-up, closing). By assessing numerous metrics of seasonal sea ice transitions, we evaluate a range of ice loss and gain processes in CMIP6 models, as well as biases that may contribute to the large spread in model projections of Arctic sea ice. We show that model biases in seasonal sea ice transitions can compensate for other unrealistic aspects of the sea ice, such as very low ice thickness, resulting in acceptable September sea ice areas for the wrong reasons. Furthermore, we find that the metrics of seasonal sea ice change, while often used interchangeably, are not related to ice area and thickness in the same ways.

How to cite: Smith, A., Jahn, A., and Wang, M.: Seasonal transitions of Arctic sea ice over the satellite era in CMIP6 models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-897, https://doi.org/10.5194/egusphere-egu2020-897, 2020.

EGU2020-7782 | Displays | CR6.2

Dissolved Neodymium Isotopes Trace Origin and Spatiotemporal Evolution of Modern Arctic Sea Ice

Georgi Laukert, Dorothea Bauch, Ilka Peeken, Thomas Krumpen, Kirstin Werner, Ed Hathorne, Marcus Gutjahr, Heidemarie Kassens, and Martin Frank

The lifetime and thickness of Arctic sea ice have markedly decreased in the recent past. This affects Arctic marine ecosystems and the biological pump, given that sea ice acts as platform and transport medium of marine and atmospheric nutrients. At the same time sea ice reduces light penetration to the Arctic Ocean and restricts ocean/atmosphere exchange. In order to understand the ongoing changes and their implications, reconstructions of source regions and drift trajectories of Arctic sea ice are imperative. Automated ice tracking approaches based on satellite-derived sea-ice motion products (e.g. ICETrack) currently perform well in dense ice fields, but provide limited information at the ice edge or in poorly ice-covered areas. Radiogenic neodymium (Nd) isotopes (εNd) have the potential to serve as a chemical tracer of sea-ice provenance and thus may provide information beyond what can be expected from satellite-based assessments. This potential results from pronounced εNd differences between the distinct marine and riverine sources, which feed the surface waters of the different sea-ice formation regions. We present the first dissolved (< 0.45 µm) Nd isotope and concentration data obtained from optically clean Arctic first- and multi-year sea ice (ice cores) collected from different ice floes across the Fram Strait during the RV POLARSTERN cruise PS85 in 2014. Our data confirm the preservation of the seawater εNdsignatures in sea ice despite low Nd concentrations (on average ~ 6 pmol/kg) resulting from efficient brine rejection. The large range in εNd signatures (~ -10 to -30) mirrors that of surface waters in various parts of the Arctic Ocean, indicating that differences between ice floes but also between various sections in an individual ice core reflect the origin and evolution of the sea ice over time. Most ice cores have εNd signatures of around -10, suggesting that the sea ice was formed in well-mixed waters in the central Arctic Ocean and transported directly to the Fram Strait via the Transpolar Drift. Some ice cores, however, also revealed highly unradiogenic signatures (εNd < ~ -15) in their youngest (bottom) sections, which we attribute to incorporation of meltwater from Greenland into newly grown sea ice layers. Our new approach facilitates the reconstruction of the origin and spatiotemporal evolution of isolated sea-ice floes in the future Arctic.

How to cite: Laukert, G., Bauch, D., Peeken, I., Krumpen, T., Werner, K., Hathorne, E., Gutjahr, M., Kassens, H., and Frank, M.: Dissolved Neodymium Isotopes Trace Origin and Spatiotemporal Evolution of Modern Arctic Sea Ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7782, https://doi.org/10.5194/egusphere-egu2020-7782, 2020.

EGU2020-11615 | Displays | CR6.2

Winter Arctic Sea Ice Volume Budget Decomposition from Satellite Observations and Model Simulations over the CryoSat-2 period (2010-2019)

Michel Tsamados, Oliver Racher, Paul Holland, Noriaki Kimura, Harry Heorton, Daniel Feltham, David Schroeder, Andy Ridout, and Julienne Stroeve

In this study, satellite-derived observations of sea ice concentration, drift, and thickness are combined to provide a climatology and inter-annual monthly variability of the sea ice volume budget over the growth season for the CryoSat-2 period Octobre 2010 to April 2019. This allows the first wintertime observational decomposition of the dynamic (advection and divergence) and thermodynamic drivers of ice volume change.

Dynamic and thermodynamic processes will be separated by applying similar methods to Holland and Kwok (2012), which decomposed the governing equation of ice concentration, C:

[1] ∂C/∂t + ∇.(uC) = f_C - r

where u is ice drift motion, f_C is thermodynamic freezing or melting, and r is the concentration change from mass-conserving mechanical ice redistribution processes which convert ice area to ice thickness, such as ridging and rafting. ∂C/∂t represents ice intensification and ∇.(uC) represents ice flux divergence, the dynamic contribution to ice concentration.

Equation 1 can be rearranged and the dynamic contribution, ∇.(uC), expanded to show the contributions from advection, (-u.∇C) and divergence, (-C∇.u), determining four terms:

[2] ∂C/∂t = -u.∇C - C∇.u + f - r

The governing equation of the volume budget is of the same form but combines the thickness and concentration data:

[3] ∂Ch/∂t = -u.∇Ch - Ch∇.u + f_Ch

where h is the thickness of the ice and the resulting product of the two datasets, Ch, is the effective thickness. If Ch were to be multiplied by the grid cell area this would give the volume, V. It is not necessary to take this step because the area remains constant and does not influence the relative values of the terms. However, when deriving an Arctic-wide climatology spatial integration across the grid cell areas is required. Ridging is taken into account by effective thickness change, therefore, it is not included in the calculations.

The method is replicated using model simulations from the Centre for Climate Observation and Modelling (CPOM)-modified Los Alamos sea-ice model (CICE), providing a test of the model’s ability to calculate the volume budgets but also identifying unrealistic growth regimes in the CryoSat-2 observational datasets. Sensitivity to several observational datasets is performed to provide an estimated uncertainty of the budget calculations.

The observational results show ice gain in the central Arctic is dominated by ice freezing with contributions from convergence. Divergence at the coastlines of the Arctic form an ice sink where freezing generates new ice. Advection is shown to drive ice equatorward and induce melting at the ice edge where ice becomes thermodynamically unstable. The dynamic components are found to grow in influence throughout the growth season.

The 2016/17 winter growth season budget shows reduced thermodynamic intensification and stronger dynamic tendencies which may be in response to thin initial ice and an exceptionally warm winter. Compared to the observed volume budget, the CICE model displays similar patterns of thermodynamic freezing, however, dynamic components in the central Arctic are significantly reduced whilst they are over-amplified at the ice edge.

How to cite: Tsamados, M., Racher, O., Holland, P., Kimura, N., Heorton, H., Feltham, D., Schroeder, D., Ridout, A., and Stroeve, J.: Winter Arctic Sea Ice Volume Budget Decomposition from Satellite Observations and Model Simulations over the CryoSat-2 period (2010-2019), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11615, https://doi.org/10.5194/egusphere-egu2020-11615, 2020.

EGU2020-21530 | Displays | CR6.2

Modelling melt ponds in Global Circulation Models

Jean Sterlin, Thierry Fichefet, François Massonnet, Olivier Lecomte, and Martin Vancoppenolle

Melt ponds appear during the Arctic summer on the sea ice cover when meltwater and liquid precipitation collect in the depressions of the ice surface. The albedo of the melt ponds is lower than that of surrounding ice and snow areas. Consequently, the melt ponds are an important factor for the ice-albedo feedback, a mechanism whereby a decrease in albedo results in greater absorption of solar radiation, further ice melt, and lower albedos 

To account for the effect of melt ponds on the climate, several numerical schemes have been introduced for Global Circulation Models. They can be classified into two groups. The first group makes use of an explicit relation to define the aspect ratio of the melt ponds. The scheme of Holland et al. (2012) uses a constant ratio of the melt pond depth to the fraction of sea ice covered by melt ponds. The second group relies on theoretical considerations to deduce the area and volume of the melt ponds. The scheme of Flocco et al. (2012) uses the ice thickness distribution to share the meltwater between the ice categories and determine the melt ponds characteristics.

Despite their complexity, current melt pond schemes fail to agree on the trends in melt pond fraction of sea ice area during the last decades. The disagreement casts doubts on the projected melt pond changes. It also raises questions on the definition of the physical processes governing the melt ponds in the schemes and their sensitivity to atmospheric surface conditions.

In this study, we aim at identifying 1) the conceptual difference of the aspect ratio definition in melt pond schemes; 2) the role of refreezing for melt ponds; 3) the impact of the uncertainties in the atmospheric reanalyses. To address these points, we have run the Louvain-la-Neuve Ice Model (LIM), part of the Nucleus for European Modelling of the Ocean (NEMO) version 3.6 along with two different atmospheric reanalyses as surface forcing sets. We used the reanalyses in association with Holland et al. (2012) and Flocco et al. (2012) melt pond schemes. We selected Holland et al. (2012) pond refreezing formulation for both schemes and tested two different threshold temperatures for refreezing. 

From the experiments, we describe the impact on Arctic sea ice and state the importance of including melt ponds in climate models. We attempt at disentangling the separate effects of the type of melt pond scheme, the refreezing mechanism, and the atmospheric surface forcing method, on the climate. We finally formulate a recommendation on the use of melt ponds in climate models. 

How to cite: Sterlin, J., Fichefet, T., Massonnet, F., Lecomte, O., and Vancoppenolle, M.: Modelling melt ponds in Global Circulation Models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21530, https://doi.org/10.5194/egusphere-egu2020-21530, 2020.

EGU2020-5812 | Displays | CR6.2

Modeling the geometry of melt ponds on Arctic sea ice

Kenneth Golden, Brady Bowen, Yiping Ma, Ryleigh Moore, Court Strong, and Ivan Sudakov

In late spring small pools of melt water on the surface of Arctic sea ice begin to grow and coalesce to form large connected labyrinthine ponds. The fractal geometry of these iconic blue patterns is both beautiful to the eye and important to the evolution of sea ice albedo and its role in the climate system. Here we report on recent results in modeling the geometry of Arctic melt ponds. We consider two models, first where pond boundaries are the level curves of random surfaces representing snow topography, and then an Ising model, originally developed a century ago to understand ferromagnetic materials, adapted to describe melt ponds. Our melt pond Ising model requires only one measured input - a length scale from snow topography data. Then energy minimization produces realistic ponds whose sizes and transition in fractal dimension with increasing area agree closely with observations. Finally we examine how the random snow topography influences the evolution of pond fractal geometry and find that the saddle points of the surface play the critical role in transitional behavior.

How to cite: Golden, K., Bowen, B., Ma, Y., Moore, R., Strong, C., and Sudakov, I.: Modeling the geometry of melt ponds on Arctic sea ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5812, https://doi.org/10.5194/egusphere-egu2020-5812, 2020.

The permeability of sea ice is an important property with regard to the role of sea ice in the earth system. It controls fluid flow within sea ice, and thus processes like melt pond drainage, desalination and to some degree heat fluxes between the ocean and the atmosphere. It also impacts the role of sea ice in hosting sea ice algae and organisms, and the uptake and release of nutrients and pollutants from Arctic surface waters. However, as it is difficult to measure in the field, observations of sea ice permeability are sparse and vary, even for similar porosity, over orders of magnitude. Here I present progress on this topic in three directions. First, I present results from numerical simulations of the permeability of young sea ice based on 3-d X-ray microtomographic images (XRT). These results provide a relationship between permeability and brine porosity of young columnar sea ice for the porosity range 2 to 25 %. The simulations also show that this ice type is permeable and electrically conducting down to a porosity of 2 %, considerably lower than what has been proposed in previous work. Second, the XRT-based simulations are compared to predictions based on a novel crystal growth modelling approach, finding good agreement. Third, the permeability model provides a relationship between sea ice growth velocity and permeability. Based on this relationshiop interesting aspects of the growth of permeable sea ice can be deduced: The predictions consistently explain observations of the onset of convection from growing sea ice. They also allow for an evaluation of expected permeability changes for a thinning sea ice cover in a warmer climate. As the model is strictly valid for growing and cooling sea ice, the results are mostly relevant for sea ice desalination processes during winter. Modelling permeability of summer ice (and melt pond drainage) will require more observations of the pore space evolution in warming sea ice, for which the present results can be considered as a resonable starting point.

How to cite: Maus, S.: Permeability of growing sea ice - observations, modelling and some implications for thinning Arctic sea ice , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5863, https://doi.org/10.5194/egusphere-egu2020-5863, 2020.

EGU2020-20328 | Displays | CR6.2

Sea-ice algal phenology in a warmer Arctic

Letizia Tedesco, Marcello Vichi, and Enrico Scoccimarro

The Arctic sea-ice decline is among the most emblematic manifestations of climate change and is occurring before we understand its ecological consequences. We investigated future changes in algal productivity combining a biogeochemical model for sympagic algae with sea-ice drivers from an ensemble of 18 CMIP5 climate models. Model projections indicate quasi-linear physical changes along latitudes but markedly nonlinear response of sympagic algae, with distinct latitudinal patterns. While snow cover thinning explains the advancement of algal blooms below 66°N, narrowing of the biological time windows yields small changes in the 66°N to 74°N band, and shifting of the ice seasons toward more favorable photoperiods drives the increase in algal production above 74°N. These diverse latitudinal responses indicate that the impact of declining sea ice on Arctic sympagic production is both large and complex, with consequent trophic and phenological cascades expected in the rest of the food web.

How to cite: Tedesco, L., Vichi, M., and Scoccimarro, E.: Sea-ice algal phenology in a warmer Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20328, https://doi.org/10.5194/egusphere-egu2020-20328, 2020.

EGU2020-8546 | Displays | CR6.2

A comparison of two alternative approaches to modelling the sea ice floe size distribution.

Adam Bateson, Daniel Feltham, David Schröder, Lucia Hosekova, Jeff Ridley, and Yevgeny Aksenov

Sea ice exists as individual units of ice called floes. These floes can vary by orders of magnitude in diameter over small spatial scales. They are better described by a floe size distribution (FSD) rather than by a single diameter. Observations of the FSD are frequently fitted to a power law with a negative exponent. Floe size can influence several sea ice processes including the lateral melt rate, momentum exchange between the sea ice, ocean and atmosphere, and sea ice rheology. There have been several recent efforts to develop a model of the floe size distribution to include within sea ice models to improve the representation of floe size beyond a fixed single value. Some of these involve significant approximations about the shape and variability of the distribution whereas others adopt a more prognostic approach that does not restrict the shape of the distribution.

In this study we compare the impacts of two alternative approaches to modelling the FSD within the CICE sea ice model. The first assumes floes follow a power law distribution with a constant exponent. Parameterisations of processes thought to influence the floe size distribution are expressed in terms of a variable FSD tracer. The second uses a prognostic floe size-thickness distribution. The sea ice area in individual floe size categories evolves independently such that the shape of distribution is an emergent behaviour rather than imposed. Here we compare the impact of the two modelling approaches on the thermodynamic evolution of the sea ice. We show that both predict an increase in lateral melt with a compensating reduction in basal melt. We find that the magnitude of this change is highly dependent on the form of the distribution for the smallest floes. We also explore the impact of both FSD models on the momentum exchange of the sea ice and find a large response in the spatial distribution of sea ice volume. Finally, we will discuss whether the results from the prognostic FSD model support the assumptions required to construct the power law derived FSD model.

How to cite: Bateson, A., Feltham, D., Schröder, D., Hosekova, L., Ridley, J., and Aksenov, Y.: A comparison of two alternative approaches to modelling the sea ice floe size distribution. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8546, https://doi.org/10.5194/egusphere-egu2020-8546, 2020.

EGU2020-18304 | Displays | CR6.2

The impact of snow products on detecting trends in sea ice thickness during the CryoSat-2 era

Heidi Sallila, Samantha Buzzard, Eero Rinne, and Michel Tsamados

Retrieval of sea ice depth from satellite altimetry relies on knowledge of snow depth in the conversion of freeboard measurements to sea ice thickness. This remains the largest source of uncertainty in calculating sea ice thickness. In order to go beyond the use of a seasonal snow climatology, namely the one by Warren created from measurements collected during the drifting stations in 1937 and 1954–1991, we have developed as part of an ESA Arctic+ project several novel snow on sea ice pan-Arctic products, with the ultimate goal to resolve for the first time inter-annual and seasonal snow variability.

Our products are inter-compared and calibrated with each other to guarantee multi-decadal continuity, and also compared with other recently developed snow on sea ice modelling and satellite based products. Quality assessment and uncertainty estimates are provided at a gridded level and as a function of sea ice cover characteristics such as sea ice age, and sea ice type.

We investigate the impact of the spatially and temporally varying snow products on current satellite estimates of sea ice thickness and provide an update on the sea ice thickness uncertainties. We pay particular attention to potential biases of the seasonal ice growth and inter-annual trends.

How to cite: Sallila, H., Buzzard, S., Rinne, E., and Tsamados, M.: The impact of snow products on detecting trends in sea ice thickness during the CryoSat-2 era, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18304, https://doi.org/10.5194/egusphere-egu2020-18304, 2020.

EGU2020-19061 | Displays | CR6.2

Towards improving radiometry-derived snow depths with SNOWPACK and SMRT

Robbie Mallett, Julienne Stroeve, Michel Tsamados, and Glen Liston

The depth of overlying snow on sea ice exerts a strong control on atmosphere-ocean heat and light flux and introduces major uncertainties in the remote sensing of sea ice thickness. Satellite-mounted microwave radiometers have enabled retrieval of snow depths over first year ice, but such retrievals are subject to a wide margin of error due to spatial variation in snow stratigraphy and roughness.

Here we model the microwave signature of snow on sea ice using a recently released sea ice variant of the snowpack evolution model, SNOWPACK (Wever et al., 2020). By advecting parcels of sea ice using ice motion vectors and exposing them to the relevant atmospheric forcing using ERA5 reanalysis, we model the accumulation of snow and the development of snowpack stratigraphy.

We then pass these modelled snowpacks to the Snow Microwave Radiative Transfer model (Picard et al., 2018) to estimate their microwave emission characteristics. By using relationships from the literature relating the ratios of the 37GHz and 19GHz channels, we calculate whether the traditional “gradient ratio” method (Markus and Cavalieri, 1998) over- or underestimates the depth of snow at a particular point based on our modelling. We then adjust the observed gradient ratio based on the model results in an attempt to better characterise snow depths.

 

References

Wever, Nander, et al. "Version 1 of a sea ice module for the physics-based, detailed, multi-layer SNOWPACK model." Geoscientific Model Development 13.1 (2020): 99-119.

Picard, Ghislain, Melody Sandells, and Henning Löwe. "SMRT: An active–passive microwave radiative transfer model for snow with multiple microstructure and scattering formulations (v1. 0)." Geoscientific Model Development 11.7 (2018): 2763-2788.

Markus, Thorsten, and Donald J. Cavalieri. "Snow depth distribution over sea ice in the Southern Ocean from satellite passive microwave data." Antarctic sea ice: physical processes, interactions and variability 74 (1998): 19-39.

How to cite: Mallett, R., Stroeve, J., Tsamados, M., and Liston, G.: Towards improving radiometry-derived snow depths with SNOWPACK and SMRT, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19061, https://doi.org/10.5194/egusphere-egu2020-19061, 2020.

EGU2020-19051 | Displays | CR6.2

Inter-comparison of snow depth over sea ice from multiple methods

Lu Zhou, Julienne Stroeve, and Shiming Xu

In this study, we compare eight recently developed snow depth products that use satellite observations, modeling or a combination of satellite and modeling approaches. These products are further compared against various ground-truth observations, including those from ice mass balance buoys (IMBs), snow buoys, snow depth derived from NASA's Operation IceBridge (OIB) flights, as well as snow depth climatology from historical observations.

Large snow depth differences between data sets are observed over the Atlantic and Canadian Arctic sectors. Among the products evaluated, the University of Washington snow depth product (UW) produces the overall deepest Spring snow packs, while the snow product from the Danish Meteorological Institute (DMI) provide the shallowest Spring snow depths. There is no significant trend for mean snow depth among all snow products since the 2000s, however, those in regional varies larhely. Two products, SnowModel-LG and the NASA Eulerian Snow on Sea Ice Model: NESOSIM, also provide estimates of snow density. Arctic-wide, these density products show the expected seasonal evolution with varying inter-annual variability, and no significant trend since the 2000s. Compared to climatology, snow density from SnowModel-LG is generally denser, whereas that from NESOSIM is less. Both SnowModel-LG and NESOSIM densities have a larger seasonal change than climatology.

Inconsistencies in the reconstructed snow parameters among the products, as well as differences and with in-situ and airborne observations can in part be attributed to differences in effective footprint and spatial/temporal coverage, as well as insufficient observations for validation/bias adjustments. Our results highlight the need for more targeted Arctic surveys over different spatial and temporal scales to allow for a more systematic comparison and fusion of airborne, in-situ and remote sensing observations.

How to cite: Zhou, L., Stroeve, J., and Xu, S.: Inter-comparison of snow depth over sea ice from multiple methods, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19051, https://doi.org/10.5194/egusphere-egu2020-19051, 2020.

EGU2020-12836 | Displays | CR6.2

Snow topography on undeformed Arctic sea ice captured by an idealized model

Predrag Popovic, Justin Finkel, Mary Silber, and Dorian Abbot

Our ability to predict the future of Arctic sea ice is limited by ice's sensitivity to detailed surface conditions such as the distribution of snow and melt ponds. Snow on top of the ice decreases ice's thermal conductivity, increases its reflectivity, and provides a source of meltwater for melt ponds during summer that decrease the ice's albedo. Here, we develop a simple model of pre-melt ice surface topography that accurately describes snow cover on flat, undeformed ice. The model considers a surface that is a sum of randomly sized and placed ``snow dunes'' represented as Gaussian mounds. This model generalizes the "void model" of Popovic et al. (2018) and, as such, accurately describes the statistics of melt pond geometry. We test this model against detailed LiDAR measurements of the pre-melt snow topography. We show that the model snow-depth distribution is statistically indistinguishable from the measurements on flat ice, while small disagreement exists if the ice is deformed. We then use this model to determine analytic expressions for the conductive heat flux through the ice and for melt pond coverage evolution during an early stage of pond formation. We also formulate a criterion for ice to remain pond-free throughout the summer. Results from our model could be directly included in large-scale models, thereby improving our understanding of energy balance on sea ice and allowing for more reliable predictions of Arctic sea ice in a future climate. 

How to cite: Popovic, P., Finkel, J., Silber, M., and Abbot, D.: Snow topography on undeformed Arctic sea ice captured by an idealized model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12836, https://doi.org/10.5194/egusphere-egu2020-12836, 2020.

EGU2020-1167 | Displays | CR6.2

A textural approach to snow depth distribution on Antarctic sea ice

M. Jeffrey Mei and Ted Maksym

Understanding the distribution of snow depth on Antarctic sea ice is critical to estimating the sea ice thickness distribution from laser altimetry data, such as from Operation IceBridge or ICESat-2.  One major uncertainty in converting laser altimetry data to ice thickness is knowing the proportion of snow within the surface measurement. Snow redistributed by wind collects around areas of deformed ice, but it is not known how different surface morphologies affect this distribution. Here, we apply a textural segmentation algorithm to classify and group similar textures to infer the distribution of snow-ice ratios using snow surface freeboard measurements from Operation IceBridge (OIB) campaigns over the Weddell Sea. We find that texturally-similar regions have similar snow/ice ratios, but not similar snow depth measurements. This allows for the extrapolation of nadir-looking snow radar data using two-dimensional surface altimetry scans, providing a two-dimensional estimate of the snow depth. Using a convolutional neural network on an in-situ dataset, we find that local (~20 m) snow depth and sea ice thickness can be estimated with errors of < 20%, and that the learned convolutional filters imply that different surface morphologies have different proportions of snow/ice within the measured surface elevation. For the OIB data,  we show that at slightly larger scales (~180 m), snow depths can be estimated using the snow surface texture, and that the learned filters are comparable to standard textural segmentation filters. We also examine the statistical variability in the distribution of snow/ice ratios across different years to determine if snow distribution patterns on sea ice exhibit universal behaviour, or have significant interannual variations. These results suggest that surface morphological information can improve remotely-sensed estimates of snow depth, and hence sea ice thickness, compared to current methods. Such methods may be useful for reducing errors in Antarctic sea ice thickness estimates from ICESat-2.

How to cite: Mei, M. J. and Maksym, T.: A textural approach to snow depth distribution on Antarctic sea ice , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1167, https://doi.org/10.5194/egusphere-egu2020-1167, 2020.

EGU2020-1715 | Displays | CR6.2

Observation and thermodynamic modeling of the influence of snow cover on landfast sea ice thickness in Prydz Bay, East Antarctica

Jiechen Zhao, Bin Cheng, Timo Vihma, Qinghua Yang, Fengming Hui, Biao Zhao, Guanghua Hao, Hui Shen, and Lin Zhang

The observed snow depth and ice thickness on landfast sea ice in Prydz Bay, East Antarctica, were used to determine the role of snow in (a) the annual cycle of sea ice thickness at a fixed location (SIP) where snow usually blows away after snowfall and (b) early summer sea ice thickness within the transportation route surveys (TRS) domain farther from coast, where annual snow accumulation is substantial. The annual mean snow depth and maximum ice thickness had a negative relationship (r = −0.58, p < 0.05) at SIP, indicating a primary insulation effect of snow on ice thickness. However, in the TRS domain, this effect was negligible because snow contributes to ice thickness. A one-dimensional thermodynamic sea ice model, forced by local weather observations, reproduced the annual cycle of ice thickness at SIP well. During the freeze season, the modeled maximum difference of ice thickness using different snowfall scenarios ranged from 0.53–0.61 m. Snow cover delayed ice surface and ice bottom melting by 45 and 24 days, respectively. The modeled snow ice and superimposed ice accounted for 4–23% and 5–8% of the total maximum ice thickness on an annual basis in the case of initial ice thickness ranging from 0.05–2 m, respectively.

How to cite: Zhao, J., Cheng, B., Vihma, T., Yang, Q., Hui, F., Zhao, B., Hao, G., Shen, H., and Zhang, L.: Observation and thermodynamic modeling of the influence of snow cover on landfast sea ice thickness in Prydz Bay, East Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1715, https://doi.org/10.5194/egusphere-egu2020-1715, 2020.

EGU2020-4472 | Displays | CR6.2

A new coupled modeling system developed for Arctic sea ice simulation and prediction

Chao-Yuan Yang, Jiping Liu, and Shiming Xu

Arctic sea ice has experienced dramatic changes for the past few decades. Recent changes in the properties of Arctic sea ice have posed significant challenges to the research community to provide sea ice predictions. To improve our capability to predict Arctic sea ice and climate, we have developed a coupled atmosphere-sea ice-ocean model configured for the Arctic with sufficient flexibility. The Los Alamos sea ice model is coupled with the Weather Research and Forecasting (WRF) Model and the Regional Ocean Modeling System (ROMS) within the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system. A series of sensitivity experiments with different physics options have been performed to determine the ‘optimal’ physics configuration that provides reasonable simulation of Arctic sea ice.

It is well known that dynamic models used to predict Arctic sea ice at short-term periods strongly depend on model initial conditions. Thus, a data assimilation that integrates sea ice observations to generate realistic and skillful model initialization is needed to improve predictive skill of Arctic sea ice. Parallel Data Assimilation Framework has been implemented into the new modeling system to assimilate SSMIS sea ice concentration, and CyroSat-2 and SMOS sea ice thickness using a localized error subspace transform ensemble Kalman filter (LESTKF). We have conducted Arctic sea ice predictions for the melting seasons of 2017 and 2018. Predictions with improved initial sea ice states show reasonably accurate sea ice evolution and small biases in the minimum sea ice extent.

Storms-induced ocean surface waves are capable of breaking pack ice into smaller floes and changing the sea ice melting rate. We have also coupled the Simulating Wave Nearshore (SWAN) with above atmosphere-sea ice-ocean coupled system and examined the impacts of wave-ice interactions on sea ice simulation. Preliminary results suggest ocean waves have direct and indirect impacts on sea ice. Direct impacts are the fracturing of ice pack and indirect impacts the change of ocean thermo-structure through the wave breaking.

How to cite: Yang, C.-Y., Liu, J., and Xu, S.: A new coupled modeling system developed for Arctic sea ice simulation and prediction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4472, https://doi.org/10.5194/egusphere-egu2020-4472, 2020.

EGU2020-2497 | Displays | CR6.2

Development and application of NMEFC Arctic Ice-Ocean Prediction System (ArcIOPS) of CHINA

Xi Liang, Fu Zhao, Chunhua Li, and Lin Zhang

NMEFC provides sea ice services for the CHINARE since 2010, the products in the early stage (before 2017) include satellite-retrieved and numerical forecasts of sea ice concentration. Based on MITgcm and ensemble Kalman Filter data assimilation scheme,  the Arctic Ice-Ocean Prediction System (ArcIOPS v1.0), was established in 2017. ArcIOPS v1.0 assimilates available satellite-retrieved sea ice concentration and thickness data. Sea ice thickness forecasting products from ArcIOPS v1.0 are provided to the CHINARE8, and are believed to have played an important role in the successful passage of R/V XUELONG through the Central Arctic for the first time during the summer of 2017. In 2019, ArcIOPS v1.0 was upgraded to the latest version (ArcIOPS v1.1), which assimilates satellite-retrieved sea ice concentration, sea ice thickness, as well as sea surface temperature (SST) data in ice free areas. Comparison between outputs of the latest version of ArcIOPS and that of its previous version shows that the latest version has a substantial improvement on sea ice concentration forecasts. In the future, with more and more kinds of observations to be assimilated, the high-resolution version of ArcIOPS will be put into operational running and benefit Chinese scientific and commercial activities in the Arctic Ocean.

How to cite: Liang, X., Zhao, F., Li, C., and Zhang, L.: Development and application of NMEFC Arctic Ice-Ocean Prediction System (ArcIOPS) of CHINA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2497, https://doi.org/10.5194/egusphere-egu2020-2497, 2020.

EGU2020-13039 | Displays | CR6.2

Sensitivity of Arctic sea ice to variable model parameter space in Regional Arctic System Model simulations.

Robert Osinski, Wieslaw Maslowski, Younjoo Lee, Anthony Craig, Jaclyn Clement-Kinney, and Jan Niciejewski

The Arctic climate system is very sensitive to the state of sea ice due to its role in controlling heat and momentum exchanges between the atmosphere and the ocean. However, the representation of sea ice state, its past variability and future projections in modern Earth system models (ESMs) vary widely. One of the reasons for that is strong sensitivity of ESMs to sea ice related varying parameter space. Based on limited observations, those parameters typically have a range of possible values and / or are not constant in space and time, which is a source of model uncertainties.   

The Regional Arctic System Model (RASM) is a limited-domain fully coupled climate model used in this study to investigate sensitivity of sea ice states to limited set of parameters. It includes the atmospheric (Weather Research and Forecasting; WRF) and land hydrology (Variable Infiltration Capacity; VIC) components sharing a 50-km pan-Arctic grid. The sea ice (the version 6.0 of Los Alamos sea ice model, CICE) and ocean (Parallel Ocean Program, POP) components share a 1/12° pan-Arctic grid. In addition, a river routing scheme (RVIC) is used to represent the freshwater flux from land to ocean. All components are coupled at high frequency via the Community Earth System Model (CESM) coupler version CPL7.

We have selected four parameters out of the set evaluated by Urrego-Blanco et al. (2016) and subject to their potential impact on sea ice and coupling across the atmosphere-sea ice-ocean interface. The total of 96 sensitivity simulations have been completed with fully coupled and forced RASM configurations, varying each parameter within its respective acceptable range. Using sea ice volume as a measure of sensitivity, the thermal conductivity of snow (ksno) parameter has produced the most sensitivity, in qualitative agreement with Urrego-Blanco et al. (2016). However, using dynamics related metrics, such as sea ice drift or deformation, other parameters, i.e. controlling the sea ice roughness and frictional energy dissipation, have been shown more important. Finally, different quantitative sensitivities to the same parameter have been diagnosed between fully-coupled and forced RASM simulations, as well as compared to the stand alone sea ice results.

How to cite: Osinski, R., Maslowski, W., Lee, Y., Craig, A., Clement-Kinney, J., and Niciejewski, J.: Sensitivity of Arctic sea ice to variable model parameter space in Regional Arctic System Model simulations., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13039, https://doi.org/10.5194/egusphere-egu2020-13039, 2020.

EGU2020-18134 | Displays | CR6.2

Using CryoSat-2 estimates to analyse sub-grid scale sea ice thickness distribution in HadGEM3 simulations for CMIP6

David Schroeder, Danny Feltham, and Michel Tsamados

A sub-grid scale sea ice thickness distribution (ITD) is a key parameterization to enable a large-scale sea ice model to simulate winter ice growth and sea ice ridging processes realistically. Recent sophisticated developments, e.g. a melt pond model, a form drag parameterization, a floe-size distribution model, fundamentally depend on the ITD. In spite of its importance, knowledge is poor about the accuracy of the simulated ITD. Here, we derive the ITD from individual Arctic sea ice thickness estimates available from the CryoSat-2 (CS2) radar altimetry mission during ice growth seasons since 2010. We bin the CS2 data into 5 ice thickness categories used by the sea ice component CICE of HadGEM3 climate simulations: (1) ice thickness h < 60 cm, (2) 60 cm < h < 1.4 m, (3) 1.4 m < h < 2.4 m, (4) 2.4 m < h < 3.6 m, (5) h > 3.6 m. Our analysis includes historical simulations and future projections with the HadGEM3-GC31 model as well as forced ocean-ice and standalone ice simulations with the same model components NEMO v3.6 and CICE v5.1.2. The most striking difference occurs regarding the annual cycle of area fraction of ice in the thickest category (> 3.6 m). According to CS2, in the Central Arctic the fraction is below 2% in October and increases to 15-40% in April. In contrast the annual cycle is weak in all simulations. The magnitude of the area fraction differs between the simulations. For simulations which agree best with CS2 for grid cell mean ice thickness, the area fraction of thick ice is around 5% constantly throughout the whole year. Potential reasons for the discrepancy are discussed and sensitivity experiments presented to study the impact of sea ice settings on the simulated ITD, e.g. ice strength parameter, parameter for participating in ridging, heat transfer coefficients.

How to cite: Schroeder, D., Feltham, D., and Tsamados, M.: Using CryoSat-2 estimates to analyse sub-grid scale sea ice thickness distribution in HadGEM3 simulations for CMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18134, https://doi.org/10.5194/egusphere-egu2020-18134, 2020.

Evaluating the performance and consistency of passive microwave (PM) sea ice concentration (SIC) products derived from different algorithms is critical since a good knowledge of the quality of the satellite SIC products is essential for their application and improvement. To comprehensively evaluate the performance of satellite SIC in long time series and the whole polar regions (both Arctic and Antarctic), in the study we examined the spatial and temporal distribution of the discrepancy between four PM satellite SIC products with the ERA-Interim sea ice fraction dataset (ERA SIC) during the period of 2015-2018. The four PM SIC products include the DMSP SSMIS with Arctic Radiation and Turbulence Interaction Study Sea Ice (ASI) algorithm (SSMIS/ASI), the GCOM-W AMSR2 with NASA Bootstrap (BT) algorithm (AMSR2/BT), the Chinese Feng Yun-3B with enhanced NASA Team (NT2) sea ice algorithm (FY3B/NT2), and the Chinese Feng Yun-3C with NT2 (FY3C/NT2) at a spatial resolution of 12.5 km.

The results show the spatial patterns of PM SIC products are generally in good agreement with ERA SIC. The comparison of monthly and annual SIC shows that the largest bias and root mean square difference (RMSD) for the PM SIC products mainly occur in summer and the marginal ice zone, indicating that there are still many uncertainties in PM SIC products in such period and region. Meanwhile, the daily sea ice extent (SIE) and sea ice area (SIA) derived from the four PM SIC products can generally well reflect the variation trend of SIE and SIA in Arctic and Antarctic. The largest bias of SIE and SIA are above 4×106 km2 when the sea ice reaches the maximum and minimum value, and the daily bias of SIE and SIA vary seasonally and regionally, which is mainly concentrated from June to October in Arctic. In general, among the four PM SIC products, the SSMIS/ASI product performs the best compared with ERA SIC though it usually underestimates SIC with a negative bias. The FY3B/NT2 and FY3C/NT2 products show more significant discrepancy with higher RMSD and bias in Arctic and Antarctic compared with the SSMIS/ASI and AMSR2/BT. The AMSR2/BT product performs much better in Antarctic than in Arctic and it always overestimates ERA SIC with a positive bias. The consistency of the four PM products concerning ERA SIC in the Antarctic region is generally superior to that in Arctic region.

How to cite: Liang, S., Zeng, J., and Li, Z.: Comparison of sea ice concentrations from ASI, BT and NT2 algorithms with ERA-Interim dataset in the Arctic and Antarctic regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4531, https://doi.org/10.5194/egusphere-egu2020-4531, 2020.

The floe size distribution (FSD) is important to the physical and biological processes in the marginal ice zone (MIZ). The FSD is controlled by ice advection, thermodynamics (lateral melting), and dynamics (winds, tides, currents and ocean swell). These thermodynamic and dynamic conditions are different between the western Arctic (e.g., Chukchi and Beaufort Seas) and the eastern Arctic (e.g., Fram Strait). For example, the MIZ in the western Arctic is strongly influenced by a warm ocean due to enhanced sea-ice albedo feedback, while the MIZ in the eastern Arctic is strongly influenced by ocean swell. We hypothesise that this regional difference can affect the FSD differently between the two regions. To address the hypothesis, we analysed the FSD data derived the images from MEDEA and synthetic aperture radar (SAR) TerraSAR-X in Chukchi Sea, East Siberian Sea and Fram Strait. Our results show that the FSD in Chukchi Sea the most dynamic as it contains a larger percentage of smaller floes and undergoes a greater interannual variability in the FSD compared to East Siberian Sea and Fram Strait. In particular, the FSD in Chukchi Sea shows a notable change before and after 2012. This change is likely attributed to the severe storm occurred in early August 2012 and the presence of thinner ice in this region.

How to cite: Wang, Y., Hwang, B., Basu, R., and Ren, J.: Regional differences in processes controlling Arctic sea ice floe size distribution in Chukchi Sea, East Siberian and Fram Strait during pre-ponding season , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5208, https://doi.org/10.5194/egusphere-egu2020-5208, 2020.

EGU2020-18117 | Displays | CR6.2

Basin-scale granular ice dynamics modelling

Jonni Lehtiranta

Current operational sea ice models solve primitive equations on a grid and treat sea ice as a continuum with smoothly varying properties. This is the same method that is used in ocean models. The continuum assumption is unrealistic for sea ice which consists of separate rigid ice floes. The assumption works best for length scales much larger than typical floe size, and worst for very small length scales.

Winter shipping in finnish ports depends on timely sea ice information on the Baltic Sea. Due to climate change, the yearly ice covered area and thermodynamic ice growth are decreasing. However, sea ice is also becoming more mobile and dynamic, especially in the Bay of Bothnia which lies in the north end of the Baltic Sea.

A particle-based granular approach is more realistic in the length scales of individual ice floes. Such models have been developed (eg. by Mark Hopkins and Agnieszka Herman) and used successfully in limited scales, such as fjords. For larger horizontal scales, they have been computationally too expensive. Using modern GPU acceleration techniques, discrete element simulation of sea ice is becoming possible in the scale required for Baltic sea basins.

This work presents an ongoing project for building a granular sea ice model for forecasting ice dynamics. This includes ice movement and deformation and describes ridge and lead formation and similar phenomena. Existing accelerated solvers are examined, and the most suitable is adapted for Baltic sea ice and applied for the Bay of Bothnia.

How to cite: Lehtiranta, J.: Basin-scale granular ice dynamics modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18117, https://doi.org/10.5194/egusphere-egu2020-18117, 2020.

EGU2020-6994 | Displays | CR6.2

Thermal convection of air in a two-layers snow cover of immobile sea ice

Petr Bogorodskii, Vasilii Kustov, and Tuomas Laurila

Sea ice, as a rule, is covered with a heat-insulating snow cover, consisting of an ice skeleton and air-saturated pores. However, the temperature difference between the sea and the atmosphere during the cold season provides favorable conditions for macroscopic air movement, which significantly reduces the thermal resistance of snow and, thereby, affects the thermal and dynamic interaction of the atmosphere with the upper layers of the sea.

Actual snow cover accumulating on the surface of sea ice has significant heterogeneity and anisotropy of geometric and thermophysical characteristics conditioned by snow density stratification. Our work is aimed to studying the occurrence of convective instability in a system of two porous layers with permeable common boundary for boundary conditions taking into account the oceanographic aspect of the problem. The analytical solution of the problem in the Darcy-Boussinesq approximation is obtained by the Galerkin method, by selecting approximations of the vertical amplitudes of dimensionless temperature and velocity perturbations that satisfy the boundary conditions of the problem. A qualitative originality of the problem is revealed in comparison with a similar problem for a homogeneous porous layer. It is shown that the stability criteria (critical filtering Rayleigh numbers) due to the difference in the thermophysical and structural properties (coefficients of thermal conductivity, porosity and air permeability) of the layers can significantly differ from each other. According to detailed measurements of the thermal structure and metric characteristics of the fixed snow-ice cover in Amba Bay (Shokalsky Strait, Severnaya Zemlya Archipelago) during Winter 2015-2016, as well as calculations of its thermodynamic evolution, the values and temporal variability of the Rayleigh numbers are estimated. By comparing the observational and modeling data, the reality of the existence of a convective heat transfer regime in the snow cover is revealed. It is concluded that it is necessary to take into account its contribution to the thermal and mass balance of sea ice during winter period.

How to cite: Bogorodskii, P., Kustov, V., and Laurila, T.: Thermal convection of air in a two-layers snow cover of immobile sea ice , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6994, https://doi.org/10.5194/egusphere-egu2020-6994, 2020.

Atmospheric blocking events in the Northern Hemishpere have been related to regional Arctic sea ice decline. During blocking events, pulses of warm and moist air enhance the radiative forcing on the sea ice in winter due to the increased longwave radiation associated with clouds. Several studies have shown that such events are related to regional sea ice concentration decline. Daily sea ice output with the latest version of CICE from the coupled Regional Arctic System model is used to study sea ice tendencies during January-February 2014. In this period there was a follow-up of a Atlantic warm moist air insturion and a Pacific warm moist air intrusion associated with surface air temperature perturbations up to 20 degrees locally.

A decline in sea ice concentration during wintertime does not neccesarily mean that ice melt has occurred. The goal of this case study is to distinguish the sea ice response between a dynamic and a thermodynamic component. In this way, we learn how much of the sea ice is advected into another region during such an event and how much the sea ice is lost due to the enhanced forcing and temperature increase.

 

 

 

How to cite: Dekker, E.: The impact of a warm moist air intrusion on dynamic and thermodynamic sea ice tendencies in the Arctic., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8418, https://doi.org/10.5194/egusphere-egu2020-8418, 2020.

EGU2020-12685 | Displays | CR6.2

Three-dimensional convection, phase change, and solute transport in mushy sea ice

Andrew Wells, James Parkinson, Dan Martin, and Richard Katz

Sea ice is a porous mushy layer composed of ice crystals and interstitial brine. The dense brine tends to sink through the ice, driving convection. Downwelling at the edge of convective cells leads to dissolution of the ice matrix and the development of narrow, entirely liquid brine channels. The channels provide an efficient pathway for drainage of the cold, saline brine into the underlying ocean. This brine rejection provides an important buoyancy forcing for the polar oceans, and causes variation of the internal structure and properties of sea ice on seasonal and shorter timescales. This process is inherently multiscale, with simulations requiring resolution from O(mm) brine-channel scales to O(m) mushy-layer dynamic scales.

 

We present new, fully 3-dimensional numerical simulations of ice formation and convective brine rejection that model flow through a reactive porous ice matrix with evolving porosity. To accurately resolve the wide range of dynamical scales, our simulations exploit Adaptive Mesh Refinement using the Chombo framework. This allows us to integrate over several months of ice growth, providing insights into mushy-layer dynamics throughout the winter season. The convective desalination of sea ice promotes increased internal solidification, and we find that convective brine drainage is restricted to a narrow porous layer at the ice-ocean interface. This layer evolves as the ice grows thicker over time. Away from this interface, stagnant sea ice consists of a network of previously active brine channels that retain higher solute concentrations than the surrounding ice. We investigate the response of ice growth and brine drainage to varying atmospheric cooling conditions, and consider the potential implications for ice-ocean brine fluxes, nutrient transport, and sea ice ecology.



How to cite: Wells, A., Parkinson, J., Martin, D., and Katz, R.: Three-dimensional convection, phase change, and solute transport in mushy sea ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12685, https://doi.org/10.5194/egusphere-egu2020-12685, 2020.

Snow plays an important role in the Arctic climate system, modulating heat transfer in terrestrial and marine environments and controlling feedbacks. Changes in snow depth over Arctic sea ice, particularly in spring, have a strong impact on the surface energy budget, influencing ocean heat loss, ice growth and surface ponding. Snow conditions are sensitive to the phase (solid or liquid) of deposited precipitation. However, variability and potential trends of rain-on snow events over Arctic sea ice and their role in sea-ice losses are poorly understood. Time series of surface observations at Utqiagvik, Alaska, reveal rapid reduction in snow depth linked to late-spring rain-on-snow events. Liquid precipitation is critical in preconditioning and triggering snow ablation through reduction in surface albedo as well as latent heat release determined by rainfall amount, supported by field observations beginning in 2000 and model results. Rainfall was found to accelerate warming and ripening of the snowpack, with even small amounts (such as 0.3mm recorded on 24 May 2017) triggering the transition from the warming phase into the ripening phase. Subsequently, direct heat input drives snowmelt, with water content of the snowpack increasing until meltwater output occurs, with an associated rapid decrease in snow depth. Rainfall during the ripening phase can further raise water content in the snow layer, prompting onset of the meltwater output phase in the snowpack. First spring rainfall in Utqiagvik has been observed to shift to earlier dates since the 1970s, in particular after the mid-1990s. Early melt season rainfall and its fraction of total annual precipitation also exhibit an increasing trend. These changes of precipitation over sea ice may have profound impacts on ice melt through feedbacks involving earlier onset of surface melt.

How to cite: Dou, T.: The impacts of liquid precipitation on sea ice surface ablation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20971, https://doi.org/10.5194/egusphere-egu2020-20971, 2020.

EGU2020-22541 | Displays | CR6.2

Landfast ice zoning from SAR imagery

Valeria Selyuzhenok, Denis Demchev, and Thomas Krumpen

Landfast sea ice is a dominant sea ice feature of the Arctic coastal region. As a part of Arctic sea ice cover, landfast ice is an important part of coastal ecosystem, it provides functions as a climate regulator and platform for human activity. Recent changes in sea ice conditions in the Arctic have also affected landfast ice regime. At the same time, industrial interest in the Arctic shelf seas continue to increase. Knowledge on local landfast ice conditions are required to ensure safety of on ice operations and accurate forecasting.  In order to obtain a comprehensive information on landfast ice state we use a time series of wide swath SAR imagery.  An automatic sea ice tracking algorithm was applied to the sequential SAR images during the development stage of landfast ice cover. The analysis of resultant time series of sea ice drift allows to classify homogeneous sea ice drift fields and timing of their attachment to the landfast ice. In addition, the drift data allows to locate areas of formation of grounded sea ice accumulation called stamukha. This information сan be useful for local landfast ice stability assessment. The study is supported by the Russian Foundation for Basic Research (RFBR) grant 19-35-60033.

How to cite: Selyuzhenok, V., Demchev, D., and Krumpen, T.: Landfast ice zoning from SAR imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22541, https://doi.org/10.5194/egusphere-egu2020-22541, 2020.

The sharp decline of Arctic sea ice in recent decades has captured the attention of the climate science
community. A majority of climate analyses performed to date have used monthly or seasonal data. Here,
however, we analyze daily sea ice data for 1979–2016 using the self-organizing map (SOM) method to further
examine and quantify the contributions of atmospheric circulation changes to the melt-season Arctic sea ice
variability. Our results reveal two main variability modes: the Pacific sector mode and the Barents and Kara
Seas mode, which together explain about two-thirds of the melt-season Arctic sea ice variability and more
than 40% of its trend for the study period. The change in the frequencies of the two modes appears to be
associated with the phase shift of the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation
(AMO). The PDO and AMO trigger anomalous atmospheric circulations, in particular, the
Greenland high and the North Atlantic Oscillation and anomalous warm and cold air advections into the
Arctic Ocean. The changes in surface air temperature, lower-atmosphere moisture, and downwelling longwave
radiation associated with the advection are consistent with the melt-season sea ice anomalies observed
in various regions of the Arctic Ocean. These results help better understand the predictability of Arctic sea ice
on multiple (synoptic, intraseasonal, and interannual) time scales.

How to cite: Yu, L. and Zhong, S.: Revisiting the Linkages between the Variability of Atmospheric Circulations and Arctic Melt-Season Sea Ice Cover at Multiple Time Scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-373, https://doi.org/10.5194/egusphere-egu2020-373, 2020.

EGU2020-576 | Displays | CR6.2

Arctic Sea Ice in the Community Earth System Model version 2 (CESM2) over the 20th and 21st Centuries

Patricia DeRepentigny, Alexandra Jahn, Marika Holland, and Abigail Smith

Over the past decades, Arctic sea ice has declined in thickness and extent and is shifting toward a seasonal ice regime. These rapid changes have widespread implications for ecological and human activities as well as the global climate, and accurate predictions could benefit a wide range of stakeholders, from local residents to governmental policy makers. However, many aspects of the polar transient climate response remain poorly understood, particularly in regard to the response of Arctic sea ice to increasing atmospheric CO2 concentration and warming temperatures. The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides a useful framework for understanding this response, and the participating climate model simulations are a powerful tool for advancing our understanding of present and future changes in the Arctic climate system.

Here we explore the current and future states of Arctic sea ice in the Community Earth System Model version 2 (CESM2), the latest generation of the CESM and NCAR’s contribution to CMIP6. We analyze changes in Arctic sea ice cover in two CESM2 configurations with differing atmospheric components: the “low-top” configuration with limited chemistry (CESM2-CAM) and the “high-top” configuration with interactive chemistry (CESM2-WACCM). We find that the two experiments show large differences in their simulation of Arctic sea ice over the historical period. The CESM2-CAM winter ice thickness distribution is skewed thin, with an insufficient amount of ice thicker than 3 m. This leads to a lower summer ice extent compared to the CESM2-WACCM and observations. In both experiments, the timing of first ice-free conditions is insensitive to the choice of future emissions scenario (known as the shared socioeconomic pathways, or SSPs, in CMIP6), an alarming result that points to the current vulnerable state of Arctic sea ice. However, if global warming stays below 1.5°C, the probability of an ice-free summer remains low, consistent with other recent studies. By the end of the 21st century, both experiments exhibit an accelerated decline in winter ice extent under the high emissions scenario (SSP5-8.5), leading to ice-free conditions for up to 8 months and an open-water period of 220 days or more depending on the region. Initial results show that the CESM2 simulates less ocean heat loss during the fall months compared to its previous version, delaying the formation of sea ice and leading to lower winter ice extent. Given that the CESM2 reaches a higher atmospheric CO2 concentration and thus warmer global and Arctic temperatures by 2100, these results suggest the presence of emerging processes associated with a state of the Arctic climate that has never been sampled before.

How to cite: DeRepentigny, P., Jahn, A., Holland, M., and Smith, A.: Arctic Sea Ice in the Community Earth System Model version 2 (CESM2) over the 20th and 21st Centuries, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-576, https://doi.org/10.5194/egusphere-egu2020-576, 2020.

EGU2020-2425 | Displays | CR6.2

Recent behavior of the Nares Strait ice arches: anomalous collapses and enhanced export of multi-year ice from the Arctic Ocean

Kent Moore, Stephen Howell, Mike Brady, Xiaoyong Xu, and Kaitlin McNeil

The ice arches that usually develop at the northern and southern ends of Nares Strait play an important role in modulating the export of multi-year sea ice out of the Arctic Ocean.   As a result of global warming, the Arctic Ocean is evolving towards an ice pack that is younger, thinner and more mobile and the fate of its multi-year ice is becoming of increasing interest to both the scientific and policy communities.  Here, we use sea ice motion retrievals derived from Sentinel-1 imagery to report on recent behaviour of these ice arches and the associated ice flux. In addition to the previously identified early collapse of the northern ice arch in May 2017, we report that this arch failed to develop during the winters of 2018 and 2019.  In contrast, we report that the southern ice arch was only present for a short period of time during the winter of 2018.  We also show that the duration of arch formation has decreased over the past 20 years as ice in the region has thinned, while the ice area and volume fluxes have both increased.  These results suggest that a transition is underway towards a state where the formation of these arches will become atypical with a concomitant increase in the export of multi-year ice accelerating the transition towards a younger and thinner Arctic ice pack.

How to cite: Moore, K., Howell, S., Brady, M., Xu, X., and McNeil, K.: Recent behavior of the Nares Strait ice arches: anomalous collapses and enhanced export of multi-year ice from the Arctic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2425, https://doi.org/10.5194/egusphere-egu2020-2425, 2020.

The ice arches that ring the northern Canadian Arctic Archipelago have historically blocked the inflow of Arctic Ocean sea ice for the majority of the year. However, annual average air temperature in northern Canada has increased by more than 2°C over the past 65+ years and a warmer climate is expected to contribute to the deterioration of these ice arches, which in turn has implications for the overall loss of Arctic Ocean sea ice. We investigated the effect of warming on the Arctic Ocean ice area flux into the Canadian Arctic Archipelago using a 22-year record (1997-2018) of ice exchange derived from RADARSAT-1 and RADARSAT-2 imagery. Results indicated that there has been a significant increase in the amount of Arctic Ocean sea ice (103 km2/year) entering the northern Canadian Arctic Archipelago over the period of 1997-2018. The increased Arctic Ocean ice area flux was associated with reduced ice arch duration but also with faster (thinner) moving ice and more southern latitude open water leeway as a result of the Canadian Arctic Archipelago’s long-term transition to a younger and thinner ice regime. Remarkably, in 2016, the Arctic Ocean ice area flux into the Canadian Arctic Archipelago (161x103 km2) was 7 times greater than the 1997-2018 average (23x103 km2) and almost double the 2007 ice area flux into Nares Strait (87x103 km2). Indeed, Nares Strait is known to be an important pathway for Arctic Ocean ice loss however, the results of this study suggest that with continued warming, the Canadian Arctic Archipelago may also become a large contributor to Arctic Ocean ice loss.

How to cite: Howell, S. and Brady, M.: Increased Arctic Ocean sea ice loss through the Canadian Arctic Archipelago under a warmer climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2728, https://doi.org/10.5194/egusphere-egu2020-2728, 2020.

EGU2020-5495 | Displays | CR6.2

Sea Ice in the Greenland Polynya in 2018 - A Study with CryoSat-2 and SMOS

Weixin Zhu, Lu Zhou, and Shiming Xu

Abstract

Arctic sea ice is a critical component in the global climate system. It affects the climate system by radiating incident heat back into space and regulating ocean-atmosphere heat and momentum. Satellite altimetry such as CryoSat-2 serves as the primary approach for observing sea ice thickness. Nevertheless, the thickness retrieval with CryoSat-2 mainly depends on the height of the ice surface above the sea level, which leads to significant uncertainties over thin ice regimes. The sea ice at the north of Greenland is considered one of the oldest and thickest in the Arctic. However, during late February - early March 2018, a polynya formed north to Greenland due to extra strong southern winds. We focus on the retrieval of sea ice thickness and snow conditions with CryoSat-2 and SMOS during the formation of the polynya. Specifically, we investigate the uncertainty of CryoSat-2 and carry out inter- comparison of sea ice thickness retrieval with SMOS and CryoSat-2/SMOS synergy. Besides, further discussion of retrieval with CryoSat-2 is provided for such scenarios where the mélange of thick ice and newly formed thin ice is present.

How to cite: Zhu, W., Zhou, L., and Xu, S.: Sea Ice in the Greenland Polynya in 2018 - A Study with CryoSat-2 and SMOS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5495, https://doi.org/10.5194/egusphere-egu2020-5495, 2020.

EGU2020-8086 | Displays | CR6.2

Evaluation of landfast ice simulations with basal stress parameterization using the Regional Arctic System Model

Jan Niciejewski, Robert Osinski, Wieslaw Maslowski, and Anthony Craig

The landfast ice (LFI) is an important component of the Arctic environment, especially in regions of shallow shelfs North of Alaska and Siberia. Its presence affects the transfer of energy between the atmosphere and the ocean. Its outer edge continuously interacts with the moving pack ice. One of the mechanisms of LFI formation – grounded ice keels, acting as anchor points – was parametrized in the version 6 of Los Alamos sea ice model (CICE) Consortium.  The parametrization is based on the bathymetry data, ice concentration and the mean ice thickness in a grid cell. It enables determination of the critical thickness, required for large ice keels to reach the bottom and calculation of the basal stress. A series of experiments using the Regional Arctic System Model (RASM) with CICEv6 has been conducted. In addition to sea ice model, RASM includes the atmosphere (WRF), ocean (POP), land hydrology (VIC), and river routing scheme (RVIC) components controlled by a flux coupler (CPL). LFI simulations using two different rheologies: elastic-visous-plast (EVP) and elastic-anisotropic-plastic (EAP) have been evaluated in the fully coupled and forced sea ice - ocean configurations.  Also, sensitivity studies with varying values of the LFI free parameters have been performed. Results are compared against landfast ice extent data from the National Snow & Ice Data Center. In the optimal configuration, including the basal stress parameterization, the model reproduces observed landfast ice in East Siberian, Laptev Sea, and along the coast of Alaska. However, some areas continue to be problematic – like the Kara Sea where LFI is underestimated and the area around the New Siberian Islands, where landfast ice growth is too high. In the former case, the ice arching might be the major landfast ice formation mechanism there, whereas in the latter case the model internal stress distribution might not be adequate to allow realistic sea ice drift between the islands.

How to cite: Niciejewski, J., Osinski, R., Maslowski, W., and Craig, A.: Evaluation of landfast ice simulations with basal stress parameterization using the Regional Arctic System Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8086, https://doi.org/10.5194/egusphere-egu2020-8086, 2020.

EGU2020-11436 | Displays | CR6.2

Using CloudSat snowfall rate observations to constrain and characterize the uncertainties of Arctic snow-on-sea-ice
not presented

Alex Cabaj, Paul Kushner, Alek Petty, Stephen Howell, and Christopher Fletcher

Snow on Arctic sea ice plays multiple—and sometimes contrasting—roles in several feedbacks between sea ice and the global climate system. For example, the presence of snow on sea ice may mitigate sea ice melt by increasing the sea ice albedo and enhancing the ice-albedo feedback. Conversely, snow can inhibit sea ice growth by insulating the ice from the atmosphere during the sea ice growth season. In addition to its contribution to sea ice feedbacks, snow on sea ice also poses a challenge for sea ice observations. In particular, snow contributes to uncertainties in retrievals of sea ice thickness from satellite altimetry measurements, such as those from ICESat-2. Snow-on-sea-ice models can produce basin-wide snow depth estimates, but these models require snowfall input from reanalysis products. In-situ snowfall measurements are absent over most of the Arctic Ocean, so it can be difficult to determine which reanalysis snowfall product is best suited to be used as input for a snow-on-sea-ice model.

In the absence of in-situ snowfall rate measurements, measurements from satellite instruments can be used to quantify snowfall over the Arctic Ocean. The CloudSat satellite, which is equipped with a 94 GHz Cloud Profiling Radar instrument, measures vertical radar reflectivity profiles from which snowfall rates can be retrieved. This instrument provides the most extensive high-latitude snowfall rate observation dataset currently available. CloudSat’s near-polar orbit enables it to make measurements at latitudes up to 82°N, with a 16-day repeat cycle, over the time period from 2006-2016.

We present a calibration of reanalysis snowfall to CloudSat observations over the Arctic Ocean, which we then apply to reanalysis snowfall input for the NASA Eulerian Snow On Sea Ice Model (NESOSIM). This calibration reduces the spread in snow depths produced by NESOSIM when different reanalysis inputs are used. In light of this calibration, we revise the NESOSIM parametrizations of wind-driven snow processes, and we characterize the uncertainties in NESOSIM-generated snow depths resulting from uncertainties in snowfall input. We then extend this analysis further to estimate the resulting uncertainties in sea ice thickness retrieved from ICESat-2 when snow depth estimates from NESOSIM are used as input for the retrieval.

How to cite: Cabaj, A., Kushner, P., Petty, A., Howell, S., and Fletcher, C.: Using CloudSat snowfall rate observations to constrain and characterize the uncertainties of Arctic snow-on-sea-ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11436, https://doi.org/10.5194/egusphere-egu2020-11436, 2020.

CR7.1 – Cryosphere change impacts on marine ecosystems and biogeochemical cycling

EGU2020-12659 | Displays | CR7.1

From ice to ocean: Understanding the impacts of melting glaciers on marine biogeochemical cycles in the Canadian Arctic Archipelago

Maya Bhatia, Stephanie Waterman, David Burgess, Patrick Williams, Megan Roberts, Charvanaa Dhoonmoon, and Erin Bertrand

When glaciers melt, they contribute significant quantities of water and ice, sediments and dissolved chemicals to the ocean. Recent efforts in Greenland and Antarctica show that both the delivery of materials to the marine environment, as well as local changes to ocean circulation induced by the input of freshwater, have the potential to profoundly impact key processes such as primary and secondary production, and by extension the biological carbon pump. Yet, extensive knowledge gaps remain about the chemical composition of glacial meltwater runoff at the ice-ocean interface, the spatial extent of its influence within coastal environs, and the mechanisms by which glaciers affect surface marine microbial communities. Nowhere are these knowledge gaps more prominent than in the Canadian Arctic Archipelago (CAA) – a region where the role of glacial meltwater in marine biogeochemical cycles is almost fully unexplored – despite the fact that it is a hotspot for glacial retreat and meltwater runoff to the ocean. Here, we conduct a regional comparative study of the nearshore coastal zone of glaciated and non-glaciated fjords and of multiple glaciers of varying type (land-terminating, tidewater) and size draining large ice caps. Our study site in Jones Sound, NU is home to the Inuit hamlet of Grise Fiord. Traditional knowledge from this community indicates that the termini of tidewater glaciers in this region are rich in wildlife, providing habitual hunting grounds for its citizens. Guided by this information, we combined shipboard measurements of temperature, salinity, turbidity, and chlorophyll a with bottle samples characterizing oxygen, sediment, carbon, nutrient, metal, and biological community composition to elucidate how these properties evolve with distance from the shore. Results from this study substantially further our understanding of glacier-ocean impacts in the CAA and beyond, while also providing data critical to accurate future projections of high-latitude marine ecosystem productivity and function in this era of climate change.

How to cite: Bhatia, M., Waterman, S., Burgess, D., Williams, P., Roberts, M., Dhoonmoon, C., and Bertrand, E.: From ice to ocean: Understanding the impacts of melting glaciers on marine biogeochemical cycles in the Canadian Arctic Archipelago , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12659, https://doi.org/10.5194/egusphere-egu2020-12659, 2020.

EGU2020-3638 | Displays | CR7.1 | Highlight

Seasonal nutrient supply and uptake in the Barents Sea

Judith Braun, Sian Henley, Marie Porter, Tim Brand, and Keith Davidson

Rapid warming has been observed across the Arctic region in recent decades, resulting in a significant reduction in sea ice extent and duration which is most pronounced in the marginal ice zone. These sea ice changes and the resultant changes in ocean mixing are affecting nutrient supply, uptake and cycling and are predicted to have large-scale consequences for the distribution and magnitude of primary production throughout the Arctic Ocean. The objective of this study is to quantify the uptake of inorganic and organic nitrogen in the Barents Sea marginal ice zone during winter, spring and summer 2018, in the context of the seasonal transition in sea ice coverage and upper ocean dynamics.

We conducted three cruises in January, April and June 2018 along a 30 °E transect covering the full range of sea ice conditions and water masses observed in the Barents Sea. We measured the concentration of inorganic and organic nitrogen compounds throughout the water column and conducted nitrogen uptake experiments on water samples taken from the euphotic zone using 15N-labelled nitrate, ammonium, urea and amino acids.

These uptake rates are used to calculate nitrate-based new production and regenerated production based on ammonium, urea and amino acids, and these calculations are used to estimate the f-ratio. Here we will present initial results on the supply of inorganic and organic nitrogen forms and their uptake rates by different phytoplankton communities at different times of year. These rates and the derived f-ratio provide a measure for productivity of the ecosystem over the winter to summer transition. We will discuss the effects of sea ice cover and water mass structure with respect to the polar front on new production and phytoplankton community composition, which play an important role in regulating the magnitude of primary production in the Barents Sea. These results will contribute to our understanding of how biological and biogeochemical processes in the Arctic may respond to ongoing changes in the physical environment as climate change proceeds.

How to cite: Braun, J., Henley, S., Porter, M., Brand, T., and Davidson, K.: Seasonal nutrient supply and uptake in the Barents Sea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3638, https://doi.org/10.5194/egusphere-egu2020-3638, 2020.

EGU2020-9393 | Displays | CR7.1

Exploring the Growing Role of Terrestrial Carbon Across North Atlantic Fjords

Craig Smeaton and William Austin

Fjords are recognized as globally significant hotspots for the burial (Smith et al., 2015) and long-term storage (Smeaton et al., 2017) of marine and terrestrially derived organic carbon (OC). By trapping and locking away OC over geological timescales, fjord sediments provide a potentially important yet largely overlooked climate regulation service. The proximity of fjords to the terrestrial environment in combination with their geomorphology and hydrography results in the fjordic sediments being subsidized with organic carbon (OC) from the terrestrial environment. This terrestrial OC (OCterr) transferred to the marine environment has traditionally be considered lost to the atmosphere in the form of CO2 in most carbon (C) accounting schemes yet globally it is estimated that 55% of OC trapped in fjord sediments is derived from terrestrial sources (Cui et al., 2016). So is this terrestrial OC truly lost? Here, we estimate the quantity of OCterr held within North Atlantic fjords with the aim of better understanding the recent and long-term role of the terrestrial environment in the evolution of these globally significant sedimentary OC stores. By understanding this subsidy of OC from the terrestrial to the marine environment we can take the first steps in quantifying the terrestrial OC stored in fjords and the wider coastal marine environment.

Cui, X., Bianchi, T.S., Savage, C. and Smith, R.W., 2016. Organic carbon burial in fjords: Terrestrial versus marine inputs. Earth and Planetary Science Letters451, pp.41-50.

Smeaton, C., Austin, W.E., Davies, A., Baltzer, A., Howe, J.A. and Baxter, J.M., 2017. Scotland's forgotten carbon: a national assessment of mid-latitude fjord sedimentary stocks. Biogeosciences.

Smith, R.W., Bianchi, T.S., Allison, M., Savage, C. and Galy, V., 2015. High rates of organic carbon burial in fjord sediments globally. Nature Geoscience8(6), p.450.

 

How to cite: Smeaton, C. and Austin, W.: Exploring the Growing Role of Terrestrial Carbon Across North Atlantic Fjords, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9393, https://doi.org/10.5194/egusphere-egu2020-9393, 2020.

EGU2020-7114 | Displays | CR7.1

Impacts of Greenland freshwater discharge on fjord productivity: a long-term perspective

Mimmi Oksman, Anna Bang Kvorning, and Sofia Ribeiro

In the past few decades, warming of the Arctic region has resulted in an abrupt increase of freshwater discharge from the Greenland Ice Sheet into its surrounding ocean. Greenland fjords are modulated by ice-ocean interactions and are very productive ecosystems that sustain important fisheries and other societal ecosystem services. While many studies are ongoing to understand seasonal and inter-annual changes, very little is known about the long-term impacts of freshwater discharge on primary producers and overall Arctic marine ecosystem functioning and structure. This long-term perspective is particularly important because freshwater runoff is expected to increase in the future along with rising atmospheric temperatures. Here, we present records from three marine sediment cores from the Godthåbsfjord that were used to reconstruct past marine productivity and freshwater discharge. The results based on diatom assemblages, BSi and TOC indicate marked fluctuations in past fjord productivity since the end of the Medieval Climate Anomaly, and periodical bursts of freshwater into the fjord resulting in a lowered productivity.

How to cite: Oksman, M., Bang Kvorning, A., and Ribeiro, S.: Impacts of Greenland freshwater discharge on fjord productivity: a long-term perspective, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7114, https://doi.org/10.5194/egusphere-egu2020-7114, 2020.

EGU2020-11144 | Displays | CR7.1

Reduced diversity and productivity of diatoms and other protists during the Early Holocene in the subarctic North Pacific

Heike H. Zimmermann, Stefan Kruse, Kathleen R. Stoof-Leichsenring, Luise Schulte, Dirk Nürnberg, Ralf Tiedemann, and Ulrike Herzschuh

Marine protists are a phylogenetically diverse group of single-celled eukaryotes that respond sensitively to changes in environmental conditions. Yet, our understanding how long-term climate variability has shaped the taxonomic composition is mostly unknown, especially of non-biomineralizing groups, such as green algae, since traditional micropaleontological studies are limited to the analysis of microfossil remains with often hardly discernable morphological differences between species (e.g. diatoms). Here we present a sedimentary ancient DNA (sedaDNA) record of the marine sediment core SO201-2-12KL, which was retrieved from the eastern continental slope of Kamchatka at 2173 m water depth (N 53.992660°, E 162.375830°) and covers the past 19.9 thousand years. We applied sedaDNA metabarcoding to 63 samples using a diatom-specific, short plastid marker that is part of the rbcL gene. Additionally, we used metagenomic shotgun sequencing on a subset of 26 samples to investigate the overall taxonomic composition of protists. Metagenomic shotgun sequencing revealed a variety of unicellular plankton groups mostly from green algae (especially Bathycoccus) and diatoms. At 11.1 cal kyr BP only single sequences assigned to green algae, diatoms and coccolithophorids could be detected. Metabarcoding showed strong variability in the richness of diatom sequence variants, which was highest during Heinrich Stadial 1 and the Younger Dryas. From about 11.4 cal kyr BP diatom taxonomic diversity strongly decreased until about 10.7 cal kyr BP. This was associated with highest taxonomic and phylogenetic turnover recorded over the past 19.9 cal kyr. Concomitant with this we recorded sequences assigned to Skeletonema subsalsum, a coastal diatom associated with low salinities or freshwater. Tentatively, as we wait for the confirmation by further sequencing, we suggest that the reduced protist diversity during the Early Holocene resulted from sea surface freshening, which led to a strengthened vertical stratification which could have reduced past productivity due to limited nutrient supply from deeper waters to the photic zone.

How to cite: Zimmermann, H. H., Kruse, S., Stoof-Leichsenring, K. R., Schulte, L., Nürnberg, D., Tiedemann, R., and Herzschuh, U.: Reduced diversity and productivity of diatoms and other protists during the Early Holocene in the subarctic North Pacific, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11144, https://doi.org/10.5194/egusphere-egu2020-11144, 2020.

EGU2020-2744 | Displays | CR7.1

BioFe delivery to the Southern Ocean through glacial systems

Kate Winter, John Woodward, Stuart Dunning, and Robert Raiswell

Glacial systems transfer sediment, rich in essential nutrients and bioavailable iron (BioFe) from continental sources to the ocean through iceberg transport, resulting in Heinrich layers during deglacial phases. The Southern Ocean is currently nutrient-rich but iron limited, so any increase in continental sediment supply could enhance primary productivity in the Southern Ocean and ultimately drawdown atmospheric CO2; potentially limiting predicted global temperature rise. The contribution of continental sediments to this negative climate feedback loop, termed the ‘Fe hypothesis’ has yet to be considered in IPCC reports. As other sources of BioFe are decreasing, global temperatures are warming, and CO2 levels are rising at glacial terminations it is now critical to assess BioFe flux through the glacial system. In this project, we use established laboratory procedures to extract nanoparticulate Fe from Antarctic sediments, recovered from nunataks, glacial moraines and debris bands in wind scoured blue ice areas in and around the Sør Rondans Mountains in East Antarctica (72°S, 24°E). These coastal margin mountains channelise ice (and entrained sediments) from the polar plateau towards the local Roi Baudouin Ice Shelf, at flow speeds of 30 – 60 m a-1. Concentrations of FeA - comprising fresh ferrihydrite (potentially bioavailable) and FeD - comprising all remaining (oxyhydr)oxide Fe are reported at all sites, with elevated concentrations along nunataks that define the edges of deep subglacial valleys which support ice flows over 2 km thick. Terrestrial surveys of these nunataks, combined with ice penetrating radar data and numerical modelling studies show how these nutrient-rich sediments are entrained and transported through the ice, from continental Antarctica, to the Southern Ocean, where ice-influenced phytoplankton blooms have been reported.

How to cite: Winter, K., Woodward, J., Dunning, S., and Raiswell, R.: BioFe delivery to the Southern Ocean through glacial systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2744, https://doi.org/10.5194/egusphere-egu2020-2744, 2020.

EGU2020-22400 | Displays | CR7.1

On the seasonal development of sea-ice microalgal communities and a forecast for downstream effects of ongoing sea-ice decline

Maria Van Leeuwe, Mairi Fenton, Ee Davey, Amber Annett, Mike Meredith, and Jacqueline Stefels

The Western Antarctic Peninsula (WAP) is one of the fastest warming oceanic regions on earth, with a recorded increase in winter temperature of 6˚C since 1950. Coinciding with the warming of shelf water the amount of sea ice that is formed over winter shows a general declining trend. The consequences of this decline for biogeochemical processes are poorly understood. Microalgal composition and production was studied in sea ice in four consecutive winters from 2013-2016, at Ryder Bay, located at the southern part of the WAP.

Sea ice was sampled over the period of ice formation in autumn until ice melt in spring. Microalgal composition was studied by means of their pigment signature and microscopy; production capacity was studied by fluorescence analyses and C13-incorporation studies. At the onset of ice formation, the sympagic algal communities consisted of a mixture of species. Over the course of winter, heterotrophic flagellates became dominant. In spring, biomass increased strongly in the bottom layers and reached a maximum concentration of more than 700 µg Chl.a l-1 in December 2014. These communities were mainly diatom-dominated. In spring, algal samples were also taken from under ice and pelagic communities. For the first time, we are able to present data that show essential differences in seeding potential of sea ice for diatom and flagellate species. The downstream effects of predicted changes in sea-ice cover and associated ice-algal communities on biogeochemical exchange processes with the marine ecosystem will be discussed.

How to cite: Van Leeuwe, M., Fenton, M., Davey, E., Annett, A., Meredith, M., and Stefels, J.: On the seasonal development of sea-ice microalgal communities and a forecast for downstream effects of ongoing sea-ice decline, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22400, https://doi.org/10.5194/egusphere-egu2020-22400, 2020.

EGU2020-21368 | Displays | CR7.1 | Highlight

Arctic sea-ice decline impacts on primary production

Letizia Tedesco, Eva Leu, Marc Macias-Fauria, Christopher J. Mundy, Dirk Notz, Janne Søreide, Malin Daase, Jakob Doerr, and Eric Stephen Post

Arctic food webs are short and relatively species poor, rendering them vulnerable to changes or perturbations at any individual trophic level. High-latitude warming represents one major source of potential perturbation to Arctic marine and terrestrial food webs, which may experience cascading effects derived from changes in primary production through so-called “bottom-up” effects. We synthesize current knowledge on i) the changing Arctic marine icescape, ii) the drivers of biological changes for Arctic marine primary production, iii) the different pulses of Arctic marine primary production, iv) patterns of marine trophic and phenological changes, and iv) some mechanisms through which sea-ice dynamics ostensibly influence terrestrial primary productivity. We deliver a set of predictions for key productivity indicators, propose a semi-quantitative model of the expected future changes in primary production in the ice-covered Arctic Ocean, and close with an overview of the challenges ahead for reaching a holistic and comprehensive understanding of the ecosystem dynamical consequences and associated impacts on human life of warming-related sea-ice decline.

How to cite: Tedesco, L., Leu, E., Macias-Fauria, M., Mundy, C. J., Notz, D., Søreide, J., Daase, M., Doerr, J., and Post, E. S.: Arctic sea-ice decline impacts on primary production, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21368, https://doi.org/10.5194/egusphere-egu2020-21368, 2020.

EGU2020-1606 | Displays | CR7.1

Hydrography and nutrient concentrations in years of contrasting sea ice conditions in the Atlantic inflow region north of Svalbard

Angelika Renner, Allison Bailey, Marit Reigstad, Arild Sundfjord, and Sigrid Øygarden

The shelf break north of Svalbard represents a major gateway for the inflow of nutrient-rich Atlantic Water (AW) to the Arctic Ocean. In this region, AW leaves the surface and subducts below Polar Surface Water (PSW). The supply of nutrients to the euphotic layer therefore varies strongly by season but also interannually, depending on e.g. rates of advection of sea ice and PSW over the AW boundary current. Additionally, the presence of sea ice can limit light availability in spring and early summer. Here, we present results from repeat sampling of hydrography, macronutrients (nitrate/nitrite, phosphate and silicic acid), and chlorophyll a along a transect at 31 E, 81.5 N in the period 2012-2017. Such time series are scarce but invaluable for investigating the range of variability in hydrography and nutrient concentrations. Measurements were done in late summer/early autumn, giving an indication of the nutrient consumption by primary producers over summer. The different years were characterised by very distinct sea ice conditions, both during the productive season and during the field campaigns. This impacted hydrography and primary production and thus nutrient concentrations in the surface and AW layers at the end of summer.

How to cite: Renner, A., Bailey, A., Reigstad, M., Sundfjord, A., and Øygarden, S.: Hydrography and nutrient concentrations in years of contrasting sea ice conditions in the Atlantic inflow region north of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1606, https://doi.org/10.5194/egusphere-egu2020-1606, 2020.

EGU2020-10718 | Displays | CR7.1

Microbial responses to the release of DOC by sea ice and glacier melting in the East Greenland System

Alba Filella Lopez de Lamadrid and Anja Engel

Freshwater discharge around Greenland has more than doubled during the last decade. Understanding the associated physical and biogeochemical impacts in the ocean is of great importance for future predictions of ocean circulation, productivity and feedbacks within the Earth system. In summer 2019 we performed several cross-shore sections passing through the highly variable environments and physical regimes along the east Greenland coastline. Microbial communities showed distinct latitudinal and meridional distributions. Water mass characteristics played a major role in controlling the abundances of organisms with few groups appearing in significant numbers in coastal (colder and fresher) waters. Surface polar waters rich in dissolved organic carbon (DOC) flow south in the East Greenland Current maintaining a high DOC signal in inshore waters. Further optical analyses on the DOC fraction will determine what fractions of this material originate from long scale transport out of the Arctic. Of particular interest was an enhanced production of gel particles rich in carbon in an area extending across Denmark Strait, from close to Scoresby Sund to north of Iceland. Significant concentrations (e.g. 80 µg X.G. eq. L-1) of these transparent exopolymer particles (TEP) were even found deeper than 100m, which is highly unusual. Given the role of TEP as a binding agent for sinking particles, enhancing the sinking of carbon in the water column, it is of interest to know why such a TEP hotspot arises. We hypothesize that it could be either related to circulation through the Strait or the timing of bloom dynamics in this region prior to our cruise.  Our main conclusion from preliminary data analysis is that the east Greenland coastal system is highly dynamic with mixed properties reflecting various degrees of mixing between southward flowing Polar Water and warmer Atlantic water masses.

How to cite: Filella Lopez de Lamadrid, A. and Engel, A.: Microbial responses to the release of DOC by sea ice and glacier melting in the East Greenland System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10718, https://doi.org/10.5194/egusphere-egu2020-10718, 2020.

EGU2020-3949 | Displays | CR7.1

Seafloor sediment supply of nutrient silicon on the Greenland margin

Hong Chin Ng, Lucie Cassarino, Rebecca Pickering, Malcolm Woodward, Samantha Hammond, and Katharine Hendry

The biogeochemical cycling of nutrient silicon (Si) in the northern high latitudes has received increasing attention over recent years. This is in large part due to the discovery of silicon limitation of diatoms over seasonal timescales, the potential role of melting glaciers in supplying a significant amount of this nutrient to the coastal ocean, and the rapid environmental changes the polar ocean is experiencing as a result of global climate warming. However, our understanding of the nutrient Si in the polar ocean is severely restricted by the lack of knowledge of the benthic Si cycling and its controlling processes, which is due to the limited number of seafloor observations in the region. In this study, we address this knowledge gap through the acquisition of sediment pore water profiles and the execution of incubation experiments on sediment cores collected from the Greenland continental margin and the Labrador Sea.

Our results indicate a net (benthic) flux of dissolved silica (DSi) out of the sediment into the overlying seawater at the study sites. A new global compilation also reveals that benthic Si flux observed at our marginal sites are substantially higher than in the open ocean. This is likely because benthic flux in the open ocean is solely maintained by molecular diffusion along a concentration gradient, while there are additional processes: pore water advection and rapid dissolution of certain siliceous sponge groups, and other reactive silica phases, that contribute to the elevated benthic Si flux on the Greenland margin. This finding has important implications for existing evaluations of oceanic Si budgets, which have not accounted for any processes other than diffusion in the global estimation of benthic Si flux. Our results also suggest that strong benthic Si flux observed on the Greenland margin, combined with wind-driven coastal upwelling, could be a significant source of this nutrient to both the diverse (benthic) sponge communities and (planktonic) diatom productivity in the region. The magnitude of this benthic cycling could potentially rival the other continental inputs of Si in the northern high latitudes, as the first estimation of total benthic Si flux from the western Greenland shelf alone (0.04–0.27 Tmol year-1) is in the same order of magnitude as the total Si export from Greenland Ice Sheet (0.2 Tmol year-1) and the pan-Arctic rivers (0.35 Tmol year-1) respectively.

How to cite: Ng, H. C., Cassarino, L., Pickering, R., Woodward, M., Hammond, S., and Hendry, K.: Seafloor sediment supply of nutrient silicon on the Greenland margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3949, https://doi.org/10.5194/egusphere-egu2020-3949, 2020.

EGU2020-9134 | Displays | CR7.1

Micronutrient export from glacier to fjord, southwest Greenland: potential impacts on open ocean primary productivity

Rachael Ward, Kathrine Hendry, Jemma L. Wadham, Jon R. Hawkings, Robert M. Sherrell, and Amber Annett

The accelerated melting of the Greenland Ice Sheet could potentially enhance fluxes of key nutrients, to the surrounding oceans, impacting marine biogeochemical processes and ecosystems. Iron (Fe) is one key micronutrient for marine phytoplankton that may be affected by this increase in meltwater flux, with high export of dissolved and particulate Fe from glacial meltwaters into fjords and a potentially significant increase in the supply of labile and potentially bioavailable Fe to the Greenlandic shelf. However, biogeochemical processing within estuarine-like fjord systems may result in depletion of nutrients, acting as a sink of micronutrients before they can reach the coastal ocean. The extent to which glacially derived micronutrients, specifically Fe, reach coastal waters remains an unanswered question.

Here, we address this question by assessing the concentration of dissolved (<0.45 µm) and labile particulate (determined using the Berger leach) bio-essential trace metals (Fe, Cd, Mn, Ni, Cu, Zn) in two contrasting glaciated fjords in southwest Greenland; one fed predominantly by marine terminating glaciers and the other by a land terminating glacier. We investigate the difference in size fractionated concentrations between fjords and the transport of these metals from stations close to glacial termini down to the fjord mouths. Our findings reveal that each micronutrient exhibits a distinctive behaviour, with some metals enhanced in meltwaters (e.g. dissolved Fe and Mn) and some depleted (e.g. dissolved Cd), relative to marine waters. The spatial variability in our dataset highlights that concentration of Fe and other trace metals (Cd, Mn, Ni, Cu, Zn) enriched in meltwaters become depleted towards the mouth of the fjords, with non-conservative loss from surface waters. Despite this depletion, the concentrations of these metals in waters that reach the coastal zone are significantly higher than typical surface ocean values, both in dissolved and labile particulate form. These data can ultimately be used in combination with a physical understanding of the fjord systems to constrain the capacity of fjords to enhance productivity downstream and deliver micronutrients into coastal and open ocean systems. Furthermore, the direct comparison of land- and marine-terminating glacial fjords could provide valuable information on the potential future impact of retreating glacial systems with enhanced melting.

How to cite: Ward, R., Hendry, K., Wadham, J. L., Hawkings, J. R., Sherrell, R. M., and Annett, A.: Micronutrient export from glacier to fjord, southwest Greenland: potential impacts on open ocean primary productivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9134, https://doi.org/10.5194/egusphere-egu2020-9134, 2020.

EGU2020-8962 | Displays | CR7.1

Silicon Cycling in Greenlandic fjords: Comparison of Marine and Land-Terminating Glaciers

Jade Hatton, Hong Chin Ng, Alexander Beaton, Lorenz Meire, and Katharine Hendry

Meltwaters from glaciers and ice sheets in the Arctic region potentially provide significant fluxes of key nutrients to downstream ecosystems, and hence recent acceleration of melting has implications for the high-latitude biogeochemical cycles. Previous work has shown that silicon (Si) exported from glacial environments also has a distinct isotopic signature compared to those in non-glacial rivers. However, the extent to which glacially-derived Si and other bioavailable nutrients reach the open ocean is much debated, due to biological uptake and complex physical processes within heterogeneous fjord environments.

We assess the impact of glacial meltwater from marine and land-terminating glaciers on fjord biogeochemistry, with a focus upon Si cycling, by sampling two fjords (Godthåbsfjord and Ameralik Fjord) in southwest Greenland over two melt seasons. We combine silicon isotope measurements with a range of complementary physical and chemical parameters to evaluate the role of glacially derived nutrients and benthic recycling on biological productivity within the two contrasting fjord environments. Data from two consecutive melt seasons also enables us to begin to assess inter-annual variability. In addition, continuous measurements of silicic acid and nitrate concentrations along Godthåbsfjord during the 2019 melt season, obtained using novel sensor technology, allow us to assess intra-annual variations in nutrient export. Our targeted field campaigns have provided a suite of nutrient, trace element and isotopic data that will improve the current understanding of the complex biogeochemical cycling within fjord environments, and allow a better assessment of the importance of glacial meltwater on nutrient export and primary productivity in downstream ecosystems.

How to cite: Hatton, J., Ng, H. C., Beaton, A., Meire, L., and Hendry, K.: Silicon Cycling in Greenlandic fjords: Comparison of Marine and Land-Terminating Glaciers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8962, https://doi.org/10.5194/egusphere-egu2020-8962, 2020.

EGU2020-853 | Displays | CR7.1

Greenland fjord productivity under climate change - multiproxy late-Holocene records from two contrasting fjord systems

Anna Bang Kvorning, Tania Beate Thomsen, Mimmi Oksman, Marit-Solveig Seidenkrantz, Christof Pearce, Thorbjørn Joest Andersen, and Sofia Ribeiro

The Greenland Ice Sheet has been losing mass at an increasing rate over the past decades due to atmospheric and oceanic warming. As a result, freshwater discharge from the Greenland Ice sheet has doubled in the last two decades and is expected to strongly increase in the future, with a large impact on the functioning of coastal marine ecosystems. While glacier runoff delivers nutrients and labile carbon into the fjords, an increase in sediment inputs is expected to have a negative impact in primary productivity, due to increased turbidity and subsequent reduction in available light for photosynthesis. Bridging modern satellite, historical and paleo-records is a key approach, as our capacity to project future scenarios requires an understanding of long-term dynamics, and insight into past warm(er) climate periods that may serve as analogues for the future. We will present results from a master’s project developed within the framework of project GreenShift: Greenland fjord productivity under climate change. Two high-resolution sediment core records from two contrasting fjord systems in NE and SW Greenland were analysed to assess the impact of Greenland Ice Sheet melt on sediment fluxes and primary productivity, focusing on the time period from the Little Ice Age until present. The overall goal of this work is to gain a better understanding of the possible linkages between GIS melt and productivity in Greenland fjord systems, with a view to improve future projections. We followed a multiproxy approach including grain-size distribution, organic carbon and biogenic silica fluxes; and dinoflagellate cyst analyses. Our preliminary results show an overall trend towards sea-surface freshening in recent decades for both fjords influenced by land-terminating (NE) and marine-terminating (SW) glaciers, alongside with important differences both in terms of sedimentary organic composition and dinoflagellate cyst assemblages.  

How to cite: Bang Kvorning, A., Beate Thomsen, T., Oksman, M., Seidenkrantz, M.-S., Pearce, C., Joest Andersen, T., and Ribeiro, S.: Greenland fjord productivity under climate change - multiproxy late-Holocene records from two contrasting fjord systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-853, https://doi.org/10.5194/egusphere-egu2020-853, 2020.

EGU2020-20051 | Displays | CR7.1

An annual cycle of diatom succession in two contrasting Greenlandic fjords: from simple sea-ice indicators to varied seasonal strategists

Tiia Luostarinen, Sofia Ribeiro, Kaarina Weckström, Mikael Sejr, Lorenz Meire, Petra Tallberg, and Maija Heikkilä

Understanding environmental factors affecting diatom species composition at seasonal resolution can contribute to the improvement of paleo sea-ice reconstruction. We recorded diatom species succession over one full year (May 2017‒May 2018) using automated sediment traps installed in two contrasting Greenlandic fjords: seasonally ice-covered Young Sound in high arctic NE Greenland and nearly sea-ice free Godthåbsfjord in subarctic SW Greenland. The two study sites had distinct seasonal regimes in terms of both sediment and diatom fluxes. In Young Sound, diatom fluxes peaked during the ice-melt in June–July (max. 880×106 valves m-2 d-1), but were very low (0.11­–12.7×106 valves m-2 d-1) for the rest of the year. The pattern was very different in Godthåbsfjord, where diatom fluxes were more stable throughout the year and at maximum 320×106 valves m-2 d-1 in summer. A total of 60 diatom taxa were present in Young Sound and 50 in Godthåbsfjord, with 19 and 22 sympagic or pelagic species, respectively. The diatom assemblage in Young Sound is strongly dominated by the pennate sea-ice species Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica, which exhibited pulse-like deposition in the trap during and after the ice melt. In Godthåbsfjord, the fluxes were dominated by resting spores of centric Chaetoceros, while the rest of the assemblage was characterized by the cold-water indicator species Detonula confervacea spore, Fragilariopsis cylindrus and Thalassiosira antarctica var. borealis spore accompanied by some warmer-water species. Some sea-ice indicator species were also observed in Godthåbsfjord, but at very low counts and throughout the year, likely transported from the inner fjord, which experiences seasonal sea-ice coverage. We show that F. oceanica, F. reginae-jahniae and F. arctica exhibit similar seasonal behaviour and are clearly linked to sea ice. On the other hand, Fragilariopsis cylindrus seems to have a more flexible niche, and is not an unequivocal ice indicator. Similarly, Pauliella taeniata has a differing niche, and does not favour our study locations probably due to its preference for lower salinities. We underscore the importance of taking into account ecological and seasonal preferences of the individual diatom species when reconstructing past sea-ice conditions qualitatively or quantitatively.

How to cite: Luostarinen, T., Ribeiro, S., Weckström, K., Sejr, M., Meire, L., Tallberg, P., and Heikkilä, M.: An annual cycle of diatom succession in two contrasting Greenlandic fjords: from simple sea-ice indicators to varied seasonal strategists, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20051, https://doi.org/10.5194/egusphere-egu2020-20051, 2020.

EGU2020-7536 | Displays | CR7.1

Glacial meltwater microbes: are there seasonal trends in exported assemblages over different catchment sizes?

Kristýna Jachnická, Tyler J. Kohler, Lukáš Falteisek, Petra Vinšová, Marie Bulínová, Jemma L. Wadham, Guillaume Lamarche-Gagnon, Andrew J. Tedstone, Jonathan R. Hawkings, Anne M. Kellerman, Karen A. Cameron, and Marek Stibal

Glaciers and ice sheets host diverse microbial life within the hydrologically connected supraglacial, englacial, and subglacial habitats. Microbial cells are collected from the entire glacial ecosystem by seasonally-generated meltwater and exported by proglacial streams. Over the course of the melt season, a subglacial drainage system develops beneath outlet glaciers from the Greenland Ice Sheet (GrIS). This system evolves from an inefficient distributed network to a more efficient channelized pathway. The extent and interconnectivity of the subglacial drainage system with the surface and sediment bed is hypothesized to differ with catchment size.

In this study, we ask whether microbial export from GrIS outlet glacier systems depend on catchment size and whether they evolve with subglacial hydrology over time. We hypothesize that larger catchments will have proportionally greater subglacial drainage, which may be reflected in a greater proportion of subglacial microbes compared to smaller catchments, where the supraglacial inputs might have a higher influence on the exported meltwater. We also expect that changes in assemblage structure are likely to coincide with the evolution of the subglacial drainage system of larger catchments as the season progresses, with supraglacial inputs increasing in importance as the channelized efficient system fully develops. To test these hypotheses, we sampled three outlet glaciers of the GrIS with different catchment sizes (from biggest to smallest: Isunnguata Sermia, Leverett and Russell glaciers) over the 2018 summer. Meltwater samples were taken at the same time each day over a period of three weeks to catch temporal patterns of microbial assemblages. DNA was extracted from samples, and 16S rRNA gene amplicons sequenced to characterize assemblage structure.

This study will help us better understand the meltwater hydrology of the GrIS by describing patterns in its microbial export and the degree of influence from supra- and subglacial systems. In this current age of glacier recession, it is furthermore important to make these characterizations as we might not have opportunity in near future to investigate them in the same unchanged environment.

How to cite: Jachnická, K., Kohler, T. J., Falteisek, L., Vinšová, P., Bulínová, M., Wadham, J. L., Lamarche-Gagnon, G., Tedstone, A. J., Hawkings, J. R., Kellerman, A. M., Cameron, K. A., and Stibal, M.: Glacial meltwater microbes: are there seasonal trends in exported assemblages over different catchment sizes?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7536, https://doi.org/10.5194/egusphere-egu2020-7536, 2020.

EGU2020-10685 | Displays | CR7.1

The Barents Sea Benthic Silica Cycle and its Sensitivity to Change: a Stable Isotopic and Reaction-Transport Model Study

James Ward, Felipe Sales de Freitas, Hong Chin Ng, Katharine Hendry, Sandra Arndt, Rebecca Pickering, Sian Henley, Rachael Ward, Christian März, and Johan Faust

Biogeochemical cycling of silicon (Si) in the high latitudes has an important influence on the marine Si budget. The Barents Sea is divided aproximately equally into Arctic and Atlantic water (ArW and AW respectively) domains.  However, increases in the temperature and inflow of AW across the Barents Sea opening is driving an expansion of the AW realm. While the sensitivity of pelagic processes pertaining to primary production is receiving increasingly more attention, less is known of the effect on the benthic Si cycle. This knowledge gap could prove integral, as the flux of Si across the sediment-water interface (SWI) from Arctic shelf sediments could be up to 20% higher than that of riverine sources. This benthic flux is largely controlled by early diagenetic processes in sediment pore waters, including biogenic silica (bSi) dissolution and authigenic precipitation.

To improve our understanding of benthic Si dynamics in the Barents Sea and examine its sensitivity to future change, we analysed pore water and sediment samples from both the AW and ArW realms between 2017-2019 for dissolved silica (dSi) concentrations and stable silicon isotopic compositions. Moreover, to determine the composition and content of bSi, as well as Si sorbed onto metal oxides, we conducted a sequential digestion of surface sediment. Following this we coupled our analyses with reaction transport modelling to further improve our mechanistic understanding of the system and to quantitatively disentangle the relative importance of these diagenetic processes to pore water Si chemistry and benthic fluxes.

Our work suggests that both interannual and spatial variability of dSi are increased in the southern, AW region of the Barents Sea. Benthic flux estimates for the southern sites have been found to more than double (~30 to 100 mmol m-2 yr-2) between cruise years, compared to a more consistent flux in the north (~80 mmol m-2 yr-2). Therefore, future Atlantification of the northern region may enance the variability of dSi supply from the benthos to bottom waters, with potential consequences for diatom productivity in the region.

How to cite: Ward, J., Sales de Freitas, F., Chin Ng, H., Hendry, K., Arndt, S., Pickering, R., Henley, S., Ward, R., März, C., and Faust, J.: The Barents Sea Benthic Silica Cycle and its Sensitivity to Change: a Stable Isotopic and Reaction-Transport Model Study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10685, https://doi.org/10.5194/egusphere-egu2020-10685, 2020.

EGU2020-8107 | Displays | CR7.1

Benthic Fe-cycling in fjord sediments enhances the reactivity of glacially derived Fe in Arctic fjords of Svalbard

Katja Laufer, Alexander Michaud, Hans Røy, and Bo Barker Jørgensen

Glacial runoff is a significant source of Fe to high-latitude marine environments. The amount and characteristics of glacially derived Fe depends on bedrock lithology, glacial comminution as well as glacier type. Because much of the Fe that comes from glaciers is in the particulate phase or will become particulate once in contact with saline and oxic fjord water, much of the glacial Fe ends up in fjord sediments in close proximity to the glaciers. Within these sediments, the glacially derived Fe undergoes redox-cycling driven by indirect (abiotic reaction with metabolic products, such as hydrogen sulfide) and direct interactions with microorganisms. This redox-cycling has the potential to alter the characteristics of the glacially derived Fe and thereby also its fate, for example if it is buried in the sediment or exported to the water column.

We investigated the amount and reactivity of Fe(III) minerals from the meltwater plume, meltwater streams, icebergs, and sediments at stations with increasing distance from the glacier in three different fjords on the west coast of Spitsbergen, Svalbard. Two of the fjords have large tidewater- glaciers at their head and possess differing bedrock lithology (Kongsfjorden and Lilliehöökfjorden). The third fjord, Dicksonfjorden, has land-terminating glaciers with a bedrock lithology similar to the glaciers at the head of Kongsfjorden, thus providing insight into the impact of glacial retreat on benthic biogeochemical processes. Results from sequential and time-course extractions showed that Fe(III)-mineral reactivity increased with distance from the glacier fronts and decreased with sediment depth at each station in all three fjords. Fe(III)-oxide reactivity from different glacial sources (meltwater plume and iceberg material from tidewater glaciers and meltwater stream material from land-terminating glaciers) differed based on source type and Fe(III) from all glacial sources was generally less reactive compared to surficial sediments distal to the glacier front. While the general trends were the same for all three fjords, based on pore water profiles of dissolved Fe, we found a lower potential for Fe-export to the water column when only land-terminating glaciers were present. This difference highlights that glacial retreat potentially impacts the function of fjord sediments as a source of Fe to the water column. We conclude that glacial runoff supplies large quantities of Fe minerals to fjord sediments, but benthic recycling of Fe by microorganisms transforms the relatively unreactive glacially-derived Fe(III)-oxides to a more reactive form. Microbially driven recycling of reactive Fe(III)-oxides in fjord sediments may play a role in liberating Fe to the water column, predominantly at the mouth of the fjord, and might represent an unquantified source of Fe to Fe-limited marine phytoplankton.

How to cite: Laufer, K., Michaud, A., Røy, H., and Jørgensen, B. B.: Benthic Fe-cycling in fjord sediments enhances the reactivity of glacially derived Fe in Arctic fjords of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8107, https://doi.org/10.5194/egusphere-egu2020-8107, 2020.

EGU2020-1528 | Displays | CR7.1

Seasonal dynamics in hydrography and biogeochemical cycling in a sub-Arctic fjord

Elizabeth Jones, Angelika Renner, Melissa Chierici, Ingrid Wiedmann, and Martin Biuw

Coastal oceans and shelf regions play a key role in marine productivity and represent an important part of the global carbon cycle, however due to strong seasonal and temporal dynamics, the processes controlling the biogeochemical cycling remain largely unresolved. This study presents the first time series measurements of hydrography, carbonate chemistry and macronutrients in a sub-Arctic fjord, Kaldfjorden (69.75 ºN, 18.68 ºE), of northern Norway during a full annual cycle. The influence of freshwater inputs and biological production were the dominant controls on fjord carbonate chemistry. Meteoric water freshened the upper layers during spring and summer, accounting for variability in surface water total alkalinity. Remineralisation of organic matter and deep mixing into carbon-rich subsurface water resupplied the water column with total inorganic carbon and macronutrients throughout the winter. Surface water saturation states (Ω) of aragonite were lowest 1.64 ± 0.04 during winter and early spring. Rapid CT drawdown in the spring phytoplankton blooms exhausted the winter stock of nitrate to drive high Ω of 2.26-2.33 and CO2 undersaturation (ΔfCO2(sea-air) was -58 ± 33 μatm) in the surface layer from April. Decreases in surface water alkalinity from July to October are consistent with coccolithophore blooms in the fjord. Kaldfjorden was estimated to be an annual net sink of atmospheric CO2. Climate change may intensify the natural variability in these important marine environments and gathering seasonal baseline data helps to unravel the contribution of fjords to oceanic CO2 cycling.

How to cite: Jones, E., Renner, A., Chierici, M., Wiedmann, I., and Biuw, M.: Seasonal dynamics in hydrography and biogeochemical cycling in a sub-Arctic fjord, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1528, https://doi.org/10.5194/egusphere-egu2020-1528, 2020.

EGU2020-17797 | Displays | CR7.1

Biomarker distributions in surface sediments of the northern Barents Sea: a basis for accurate palaeo sea-ice reconstructions

Anna J. Pienkowski, Katrine Husum, Simon Belt, and Lukas Smik

An understanding of modern sea-ice proxy distributions relative to measured environmental parameters underpins accurate palaeo reconstructions necessary for correct future projections. We here present new data on highly-branched isoprenoid (HBI) lipid biomarkers produced by sea-ice diatoms (IP25, IPSO25) and phytoplankton (HBI III, HBI IV) in marine surface sediments taken in a south-north transect east of Svalbard as part of the Nansen Legacy project. Collectively, these biomarkers can be used to reconstruct seasonal spring sea-ice (SpSIC) and the seasonal sea-ice edge. Eight sites at ~78-83°N were sampled by multicorer. All cores contain abundant biomarkers, except the northernmost station. Biomarker-based SpSIC shows a general south-north increase, mimicking observational sea-ice concentration satellite-based means (1988-2017). The HBI T25 index suggests ice edge phytoplankton blooms at southern stations, agreeing with the general pattern of increased phytoplankton HBIs previously reported from the eastern Barents Sea. As a next step, these new biomarker findings will be used to reconstruct longer-term (Holocene) variability in sea-ice in this region. 

How to cite: Pienkowski, A. J., Husum, K., Belt, S., and Smik, L.: Biomarker distributions in surface sediments of the northern Barents Sea: a basis for accurate palaeo sea-ice reconstructions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17797, https://doi.org/10.5194/egusphere-egu2020-17797, 2020.

EGU2020-13904 | Displays | CR7.1

PAGES ACME Working Group - Arctic Cryosphere Change and Coastal Marine Ecosystems

Maija Heikkilä, Anna Pieńkowski, Sofia Ribeiro, and Kaarina Weckström

The Arctic cryosphere is changing rapidly due to increased runoff from land, changing sea-ice regime and the degradation of the circumpolar permafrost zone. Fjords and other nearshore areas form a productive zone that is vital for both Arctic biodiversity and local communities, rendering the understanding of Arctic coastal ecosystem change from a long-term perspective crucial.

The ACME working group provides a community platform to critically assess and refine available coastal marine proxies that can be used to reconstruct cryosphere changes and their multifaceted ecosystem impacts. ACME seeks to promote a leap forward in the accuracy of paleo reconstructions that are central for deciphering cryosphere-biosphere interactions in the Arctic region at relevant timescales.

The goals for the three-year (2019‒2022) Phase I of the working group are:

- To build a community-refined database that contains a network of proxies commonly used for sea ice, primary production, and meltwater runoff reconstructions in Arctic coastal and fjord environments.

- To facilitate knowledge transfer and collaborations between proxy specialists and the integration of the field and satellite monitoring community.

- To further critical methodological understanding and data handling skills of the next-generation of Arctic paleoceanographers and paleoenvironmental researchers.

How to cite: Heikkilä, M., Pieńkowski, A., Ribeiro, S., and Weckström, K.: PAGES ACME Working Group - Arctic Cryosphere Change and Coastal Marine Ecosystems , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13904, https://doi.org/10.5194/egusphere-egu2020-13904, 2020.

EGU2020-11519 | Displays | CR7.1

Contributions of dinoflagellate cysts and ciliates to the sediment flux in the Beaufort Sea (Arctic Ocean): one year sediment trap record

Vera Pospelova, Catherine Lalande, Maija Heikkilä, and Louis Fortier

Studies of dinoflagellate cysts or ciliates in sediment traps provide essential information on weekly, monthly, seasonal, annual, and/or multi-annual changes in their fluxes in relation to measured or implied environmental parameters. Such information is essential for understanding ecological preferences of individual taxa which is the foundation for performing reliable (paleo)environmental high-resolution regional reconstructions. Up to date, sediment trap studies are rare, and only three of those deal with dinoflagellate cysts production in ice-covered conditions: in Antarctic waters (Harland and Pudsey, 1999); Arctic fjords in the Svalbard archipelago (Howe et al., 2010); and Hudson Bay (Heikkilä et al., 2016). All these studies consistently show a very limited or no cyst recovery from the samples that were collected during the ice-covered intervals. However, the timing of individual species production (e.g. cysts of Pentapharsodinium dalei, Islandinium minutum, and Spiniferites elongatus) within the ice-free condition is inconsistent as it varies from region to region. In this session, we will present our preliminary results on dinoflagellate cyst continuous bi-weekly record at the Beaufort Sea shelf break from September 2014 to August 2015.

How to cite: Pospelova, V., Lalande, C., Heikkilä, M., and Fortier, L.: Contributions of dinoflagellate cysts and ciliates to the sediment flux in the Beaufort Sea (Arctic Ocean): one year sediment trap record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11519, https://doi.org/10.5194/egusphere-egu2020-11519, 2020.

EGU2020-1193 | Displays | CR7.1

The biological darkening of the Greenland Ice Sheet: impacts of visible and UV light on the photosynthetic performance, metabolome and transcriptome of glacier algae

Laura Halbach, Liane G. Benning, Eva L. Doting, Martin Hansen, Hans Jakobsen, Lars C. Lund-Hansen, Lumi Haraguchi, Brian K. Sorrell, Thanassis Zervas, and Alexandre M. Anesio

Large blooms of purple-brownish pigmented glacier algae cover the ablation zones of the Greenland Ice Sheet (GrIS) and amplify its melt by lowering the ice surface albedo and increasing its solar radiation absorption. The darkening effect of these Zygnematophycean algae can be mainly attributed to their phenolic pigments, which absorb in the visible (VIS) and UV light ranges. Currently, a mechanistic understanding of the factors regulating the production of these pigments and their implications for the large-scale biologically-driven albedo reduction on the GrIS is missing. Here, we reveal how light (VIS vs. UV range) controls the phenolic pigment production, endo- and exometabolome, gene expression and photosynthetic performance of glacier algae. Two different algal communities (a mixed natural microbial community collected from snow-free ice and a laboratory-grown community of the ice algae Mesotaenium berggrenii without its original dark pigmentation) were used for a set of in situ incubations on Mittivakkat glacier in SE-Greenland. Pulse-amplitude-modulated (PAM) fluorometry revealed an overall higher photosynthetic performance (electron transport rate) at higher irradiances for the field population containing purpurogallin-like pigments compared to the lab community without dark pigmentation. The lab population showed a low maximum quantum efficiency of photosystem II under in situ light conditions, indicating a photo-damaging effect from high intensities of UV light in the absence of purpurogallin-derived phenolic pigments. Our study highlights the intracellular shading effect by purpurogallin-derived pigments, which are key for the survival of glacier algae on the ice and forms a cornerstone of understanding the large-scale variability in the biological darkening of the GrIS.

How to cite: Halbach, L., Benning, L. G., Doting, E. L., Hansen, M., Jakobsen, H., Lund-Hansen, L. C., Haraguchi, L., Sorrell, B. K., Zervas, T., and Anesio, A. M.: The biological darkening of the Greenland Ice Sheet: impacts of visible and UV light on the photosynthetic performance, metabolome and transcriptome of glacier algae , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1193, https://doi.org/10.5194/egusphere-egu2020-1193, 2020.

EGU2020-10968 | Displays | CR7.1

Diversity and strength of ice-related dimethyl sulfide sources in the Arctic

Maurice Levasseur, Martine Lizotte, Virginie Galindo, Margaux Gourdal, and Michel Gosselin

Biogenic sources of sulfur are important precursors of aerosols in the Arctic during the summer months. Recent studies show that peaks in ultrafine particle formation events often coincide with hotspots of dimethyl sulfide (DMS) emissions from the marginal ice zone. During the last 10 years, we explored the diversity of DMS sources associated with the ice and at the marginal ice zone in the Canadian Arctic, and assessed how the projected changes in sea ice extent, thickness, and other properties could strengthen or weaken these emissions. Results from four Arctic expeditions presenting DMS concentrations and dynamics in snow, sea ice, melt ponds, under-ice water, and at the ice edge will be shown and discussed in the context of ongoing and future changes in the cryosphere. The analysis of the pooled dataset points toward an increase in DMS emissions in a warmer Arctic with a potential cooling feedback on climate.

How to cite: Levasseur, M., Lizotte, M., Galindo, V., Gourdal, M., and Gosselin, M.: Diversity and strength of ice-related dimethyl sulfide sources in the Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10968, https://doi.org/10.5194/egusphere-egu2020-10968, 2020.

EGU2020-8940 | Displays | CR7.1

Iron transport by subglacial meltwater indicated by stable iron isotopes in fjord sediments of King George Island, Antarctica

Jan Hartmann, Susann Henkel, Sabine Kasten, Adrián Silva Busso, and Michael Staubwasser

Polar regions are critical for future climate evolution, and they experience major environmental changes. A particular focus of biogeochemical investigations in these regions lies on iron (Fe). This element drives primary productivity and, thus, the uptake of atmospheric CO2 in vast areas of the ocean. Due to the Fe-limitation of phytoplankton growth in the Southern Ocean, Antarctica is a key region for studying the change of iron fluxes as glaciers progressively melt away. The respective climate feedbacks can currently hardly be quantified because data availability is low, and iron transport and reaction pathways in Polar coastal and shelf areas are insufficiently understood. We show how novel stable Fe isotope techniques, in combination with other geochemical analyses, can be used to identify iron discharges from subglacial environments and how this will help us assessing short and long term impacts of glacier retreat on coastal ecosystems.

Stable Fe isotopes (δ56Fe) may be used to trace Fe sources and reactions, but respective data availability is low. In addition, there is a need to constrain δ56Fe endmembers for different types of sediments, environments, and biogeochemical processes.

δ56Fe data from pore waters and sequentially extracted solid Fe phases at two sites in Potter Cove (King George Island, Antarctica), a bay affected by fast glacier retreat, are presented. Close to the glacier front, sediments contain high amounts of easily reducible Fe oxides and show a dominance of ferruginous conditions compared to sediments close to the ice-free coast, where surficial oxic meltwater discharges and sulfate reduction dominates. We suggest that high amounts of reducible Fe oxides close to the glacier mainly derive from subglacial sources, where Fe liberation from comminuted material beneath the glacier is coupled to biogeochemical weathering. A strong argument for a subglacial source is the predominantly negative δ56Fe signature of reducible Fe oxides that remains constant throughout the ferruginous zone. In situ dissimilatory iron reduction (DIR) does not significantly alter the isotopic composition of the oxides. The composition of the easily reducible Fe fraction therefore suggests pre-depositional microbial cycling as it occurs in subglacial environments. Sediments influenced by oxic meltwater discharge show downcore trends towards positive δ56Fe signals in pore water and reactive Fe oxides, typical for in situ DIR as 54Fe becomes less available with increasing depth.

We found that a quantification of benthic Fe fluxes and subglacial Fe discharges based on stable Fe isotope geochemistry will be complicated because (1) diagenetic processes vary strongly at short lateral distances and (2) the variability of δ56Fe in subglacial meltwater has not been sufficiently well investigated yet. However, isotope mass balance models that consider the current uncertainties could, in combination with an application of ancillary proxies, lead to a much better quantification of Fe inputs into polar marine waters than currently available. This would consequently allow a better assessment of the flux and fate of Fe originating from the Antarctic Ice Sheet.

Henkel et al. (2018) Diagenetic iron cycling and stable Fe isotope fractionation in Antarctic shelf sediments, King George Island. GCA 237, 320-338.

How to cite: Hartmann, J., Henkel, S., Kasten, S., Busso, A. S., and Staubwasser, M.: Iron transport by subglacial meltwater indicated by stable iron isotopes in fjord sediments of King George Island, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8940, https://doi.org/10.5194/egusphere-egu2020-8940, 2020.

EGU2020-3917 | Displays | CR7.1

The Ecology of Antarctic Blue Ice: The BIOICE Project

Aga Nowak, Andy Hodson, Stephen Hudson, Elisabeth Isaksson, Arwyn Edwards, David Pearce, and Sara Rassner

This poster describes new studies into the microbial ecosystems found in Blue Ice Areas (BIA) around the periphery of the Antarctic Ice Sheet. These habitats are located on the Antarctic fringe, often at high elevation, and therefore represent the first opportunity for cells entombed in old glacier ice advected from Antarctic interior, to be revived by the increased availability of solar radiation (blue ice) and water (subsurface melt).

Our study is the first to consider how two different types of BIA host two different habitats; those associated with nunataks or mountain ranges, and those associated with ice surfaces only. The difference between them is the availability of debris and water for microbial processes. In the former scenario, debris is blown onto the blue ice from local sources to provide a source of both microorganisms and energy. In the latter case, the lack of an external debris source is compensated by the possibility subsurface melting due to the optical properties of blue ice. In these systems a far greater proportion of the cells are liberated from ancient glacier ice.

To explore these overlooked ecosystems, we visited high elevation (c.1200m) BIAs in Dronning Maud Land, near Troll Research Station. Our expedition during Antarctic summer season 2019-2020 yielded microbial and biogeochemical data from both debris-free and debris-rich BIAs, as well as shallow glacier ice cores of different ages. In addition, we explored a variety of cryoconite holes entombed within the above BIAs.

Our results show that BIA ecosystems are characterized by tremendous heterogeneity between their cryoconite holes. While some show signs of photosynthesis, others are dominated by bacterial production. Furthermore, optical properties of the BIA and physical properties of the ice itself (fracturing) control subsurface meltwater production and water movement, influencing the sub-ice ecosystems and their biogeochemistry.  The poster will present how we are exploring the revival of these ice bound organisms on their way from the Antarctic Ice Sheet interior towards the coast.

How to cite: Nowak, A., Hodson, A., Hudson, S., Isaksson, E., Edwards, A., Pearce, D., and Rassner, S.: The Ecology of Antarctic Blue Ice: The BIOICE Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3917, https://doi.org/10.5194/egusphere-egu2020-3917, 2020.

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